alstom pd521

-30

3 -402 -602

with Documentation for

Version -303 -402 -502

are used as connecting leads, wire end ferrules must be employed.

Proper and safe operation of this device depends on appropriate shipping and handling, proper storage, installation and commissioning, and on careful operation, maintenance and servicing. For this reason only qualified personnel may work on or operate this device.

Qualified Personnel

o are familiar with the installation, commissioning and operation of the device and of the system to which it is being connected;

o are able to perform switching operations in accordance with safety engineering standards and are authorized to energize and de-energize equipment and to isolate, ground and label it;

o are trained in the care and use of safety apparatus in accordance with safety engineering standards; o are trained in emergency procedures (first aid).

Note

The operating manual for this device gives instructions for its installation, commissioning and operation. However, the manual cannot cover all conceivable circumstances or include detailed information on all topics. In the event of questions or specific problems, do not take any action without proper authorization. Contact the appropriate ALSTOM technical sales office and request the necessary information.

Any agreements, commitments, and legal relationships and any obligations on the part of ALSTOM, including settlement of warranties, result solely from the applicable purchase contract, which is not affected by the contents of the operating manual.

The special version -303 -402 -502 incorporates an extended operating frequency range for the voltage memory and the power swing blocking function in addition to the features and functions of the standard versions -302/-303 -401/-402 -602.

Distance Protection

Distance and Directional Measurement

The frequency range of the voltage memory is extended. The voltage memory is enabled, if the measured

frequency satisfies the following condition: 0.95 f× _nom < <f 1.05 f× _nom

Power Swing Blocking

When power swing blocking is activated, a distance trip in zones 1 to 5 is prevented if there are power swings in the network.

Three-pole distance protection starting with and without ground initiates the start delay of the power swing blocking function. The start delay is intended to enable release in zone 1. After the settable start delay has elapsed, the device checks to determine whether the phase-to-phase voltage 1V_A-B is greater than 0 1. × Vnom. If this condition is satisfied, then the apparent power S is calculated from the quantities 1V_{A-B and IA-B} . The amount of change in apparent power as referred to the apparent power at that moment is determined every 40 ms.

S1 S2 S2

-S₁: apparent power at time t₁

S₂: apparent power at time t₁ + 40 ms

If the difference is greater than the set value, a blocking signal is formed to block the distance trip for zones 1 to 5. This signal is extended by the settable release delay. Power swing blocking is blocked if the monitoring function of the voltage-measuring circuit operates.

The new Addresses related to the Power Swing Blocking function are as follows: Setting parameters

Address x y

Description Change Default Range of Values Unit or Meaning

Incre-ment 14 50 PSB: Enabled on 0 0 / 1 no / yes 14 52 PSB: Start delay on 0.20 0.06 ... 1.00 s 0.01 14 53 PSB: Release delay on 0.20 0.06 ... 1.00 s 0.01 14 54 PSB: Threshold value on 25 1 ... 50 % 1 State Signals Address x y

Description Change Default Range of Values Unit or Meaning

Incre-ment

36 32 PSB: Blocking initiated - 0 / 1 no / yes

36 58 PSB: Start delay running - 0 / 1 no / yes

1 Application and Scope 7 2 Technical Data 8 2.1 Conformity Statement 8 2.2 General Data 8 2.3 Tests 8 2.3.1 Type Tests 8 2.3.2 Routine Tests 9 2.4 Environmental Conditions 9

2.5 Inputs and Outputs 10

2.6 Interfaces 10 2.7 Information Output 11 2.8 Settings 11 2.9 Typical Characteristics 11 2.10 Deviations 11 2.11 Power Supply 12 3 Operation 13 3.1 Modular Structure 13 3.2 Man-Machine Communication 13 3.3 Distance Protection 14 3.3.1 Starting 16

3.3.2 Selection of Measured Variables 24

3.3.3 Distance and Directional Measurement 25

3.3.4 Impedance-Time Characteristics 34

3.4 Measuring Circuit Monitoring 42

3.5 Backup Overcurrent-Time Protection

(BUOC or Backup DTOC) 46

3.6 Switch on to Fault Protection 47

3.7 Protective Signaling 48

3.8 Circuit Breaker Failure Protection 56

3.9 Ground Fault Direction Determination

Using Steady-State Values 56

3.9.1 GFD Evaluation (Ground Fault Direction) 57

3.9.2 GF Evaluation (Ground Fault) 61

3.9.3 Ground Fault Data Acquisition 62

3.10 Starting Signals and Tripping Logic 65

3.11 Overcurrent Signal 67

3.12 Operating Data Measurement 68

3.13 Fault Recording 71

3.13.1 Fault Logging 73

3.13.2 Measured Fault Data 73

4 Design 82

5 Installation and Connection 84

5.1 Unpacking and Packing 84

5.2 Checking Nominal Data and Design Type 84

5.3 Location Requirements 84

5.4 Installation 85

5.5 Protective and System Grounding 87

5.6 Connection 87

5.6.1 Measuring and Auxiliary Circuits 87

5.6.2 Binary Control Inputs 93

5.6.3 Tripping and Signaling Circuits 93

5.6.4 PC Interface 93

5.6.5 ILSA Interface 93

6 Control 94

6.1 Display and Keyboard 94

6.2 Address Selection 95

6.3 Change-Enabling Function 95

6.4 Changing Settings 96

6.5 Memory Readout 97

6.5.1 Signal Memory Readout 97

6.5.2 Monitoring Signal Memory Readout 99

6.6 Resetting 100

6.7 Password-Protected Control Operations 101

6.8 Keyboard Lock 102 7 Settings 103 7.1 Device Identification 103 7.1.1 Ordering Information 103 7.1.2 Design Version 104 7.2 Configuration Parameters 104 7.2.1 Control Interfaces 104 7.2.2 Binary Inputs 106 7.2.3 Binary Outputs 106 7.2.4 LED Indicators 107 7.3 Function Parameters 107 7.3.1 Global 107 7.3.2 Main Functions 108 7.3.3 Supplementary Functions 111

9 Commissioning 122

10 Troubleshooting 137

11 Maintenance 140

12 Storage 143

13 Accessories and Spare Parts 144

14 Ordering Information 145

PD 521 distance protection devices are used for selective short-circuit protection in high-voltage systems.

The systems can be operated with impedance grounding, with ground fault compensation or with isolated neutral. The PD 521, a single-system distance protection device, has the following protective functions:

¨ Overcurrent fault detection logic with optional undervoltage fault detection logic

¨ Underimpedance fault detection logic with load blinding

¨ Distance measurement with selection of polygonal or circular characteristic

¨ Four distance stages, including one that can be used as a special stage

¨ Six timer stages, including two that act as backup timer stages

¨ Direction voltage memory

¨ Circuit breaker failure protection

¨ Switch on to fault protection

¨ Backup overcurrent time protection (Backup DTOC)

¨ Protective signaling (teleprotection)

¨ Ground fault direction determination using steady-state values

Besides the functions listed above, as well as measuring circuit monitoring and comprehensive self-monitoring, the following functions are always available in the PD 521 for optimum fault evaluation and system management:

¨ Measuring circuit monitoring

¨ Operating data measurement

¨ Event counting

¨ Ground fault data acquisition

¨ Time-tagged fault logging

¨ Fault data acquisition (including fault localization)

¨ Fault recording

The PD 521 has a multifunctional case design that is equally well suited to either wall surface mounting or flush panel mounting due to the reversible terminal blocks and adjustable mounting brackets. The auxiliary voltage for the power supply can be switched internally from 110-250 V DC or 100-230V AC to 24-60 V DC. The PD 521 has the following inputs and outputs: o 4 current-measuring and 3 voltage-measuring inputs o 2 binary signal inputs (optical couplers) with freely

configurable function assignment

o 8 output relays with freely configurable function assignment

Control and display: o Local control panel

o 12 LED indicators, 9 of which allow freely configurable function assignment

2.1 Conformity Statement

Applicable to the PD 521, version 302-402/403/404-604

Article 10 of EC Directive 72/73/EC.

The product designated as "PD 521 Distance Protection Device" has been developed and manufactured in

conformity with the international standard EN 60255-6 and in accordance with the EMC Directive and the Low

Voltage Directive issued by the European Community.

2.2 General Data

Design

Case suitable for surface or flush mounting Installation position

Vertical ± 30°

Degree of device protection

IP 51 according to DIN VDE 0470 and EN 60529 or IEC 529

Weight Approx. 4.0 kg

Dimensions and connections

See Dimensional Drawings and Terminal Connection Diagrams

PC interface

Connector DIN 41 652, type D-Sub, 9-pin

A special connecting cable is required for electrical isolation.

ILSA Interface (optional)

Optical fibers (-X7 and -X8): optical fiber interface F-SMA. Leads (-X9): Mini Combicon MC 1.5/5-STF-3.81 for wire cross-sections up to 1.5 mm2 _flexible.

Connections

Threaded terminal ends M4,

self-centering with wire protection for conductor cross-sections from 0.5 mm² to 6 mm² or 2 ´ 2.5 mm²

2.3 Tests

2.3.1 Type Tests

All tests according to EN 60255-6§ and DIN 57 435 Part 303

Electromagnetic Compatibility (EMC)

Interference suppression

According to EN 55022 and DIN VDE 0878 Part 3, class B

1 MHz burst disturbance test

According to IEC 255§ Part 22-1, class III Common mode test voltage: 2.5 kV Differential test voltage: 1.0 kV

Test duration: > 2 s

Source impedance: 200 W

Immunity to electrostatic discharge

According to EN 60801§ Part 2, severity level 3 Contact discharge,

Single discharges: > 10

Holding time: > 5 s

Test voltage: 6 kV

Test generator: 50 to 100 MW, 150 pF/330 W Immunity to radiated electromagnetic energy

According to ENV 50140§_{, level 3}

Antenna distance to tested device: > 1 m on all sides Test field strength, frequ. band 80 to 1000 MHz: 10 V/m Test using AM: 1 kHz / 80 %

Single test at 900 MHz: AM 200 Hz / 100 % Electrical fast transient / burst requirements According to IEC 801-4, test severity level 3 Rise time of one pulse: 5 ns

Impulse duration (50% value): 50 ns Amplitude: 2 kV / 1 kV

Burst duration: 15 ms Burst period: 300 ms Source impedance: 50 W

Surge immunity test

According to IEC 1000-4-5, test level 3 Testing of power supply circuits,

unsymmetrically / symmetrically operated lines Open-circuit voltage front time /

/ time to half-value: 1.2 / 50 ms Short-circuit current front time / / time to half-value: 8 / 20 ms Amplitude: 1 / 2 kV

Pulse frequency: > 5 / min Source impedance: 12 / 42 W

Immunity to conducted disturbances induced by radio frequency fields

According to IEC 65A/77B (Sec) 145/110, test level 2 Disturbing test voltage: 3 V

Power frequency magnetic field immunity According to EN 61000-4-8§, level 4 Frequency: 50 Hz

Test field strength: 30 A/m

Interruptions to and alternating component (ripple) in d.c. auxiliary energizing quantity of measuring relays According to IEC 255-11 12% / 50 ms Insulation Voltage test According to IEC 255-5 2 kV AC, 60 s

For the voltage test of the power supply inputs, direct voltage (2.8 kV DC) must be used.

The PC interface must not be subjected to the voltage test.

Impulse voltage withstand test According to IEC 255-5 Front time: 1.2 µs Time to half-value: 50 µs Peak value: 5 kV Source impedance: 500 W Mechanical Robustness Vibration test

According to IEC 255-21-1§, test severity class 1 Frequency range, in operation:

10 to 60 Hz, 0.035 mm, 60 to 150 Hz, 0.5 g

Frequency range, during transport: 10 to 150 Hz, 1 g

Shock response and withstand test, bump test According to IEC 255-21-2§, test severity class 1 Acceleration: 5 g/15 g

Pulse duration: 11 ms Seismic test

According to EN 60255-21-3§,test procedure A, class 1 5 to 8 Hz, 3.5/1.5 mm,

8 to 35 Hz, 10/5 m/s2 3 ´ 1 cycle

2.3.2 Routine Tests

All tests according to EN 60255-6§ _and

DIN 57 435 Part 303 Additional thermal test

100 % controlled thermal endurance test, inputs loaded

2.4 Environmental Conditions

Allowable ambient temperatures Operating temp.: - 5 °C to + 55 °C (+ 23 °F to + 131 °F) Storage temp.: - 25 °C to + 55 °C (- 13 °F to + 131 °F) Shipping temp.: - 25 °C to + 70 °C (- 13 °F to + 158 °F) Ambient humidity range

2.5 Inputs and Outputs Measurement Inputs

Current

Connection to current transformers

Nominal current I_nom (per order): 1 A AC or 5 A AC Load rating, continuous: 4 I_nom

for 10 s: 30 I_nom for 1 s: 100 I_nom Rated surge current: 250 I_nom

Nominal consumption: < 0.3 VA per phase at I_nom Voltage

Connection to voltage transformers Nominal voltage V_nom: 100 V AC

Suitable for connection to transformers with V_nom = 100 to 130 V AC

Load rating, continuous: 1.5 V_nom

Nominal consumption: < 0.3 VA per phase at V_nom Frequency

Nominal frequency f_nom: 50 Hz or 60 Hz (settable) Operating range: 0.95 to 1.05 f_nom

Dynamic range

For the three phase currents at 1 A or 5 A: 100 I_nom For the residual current at 1 A or 5 A: 10 I_nom

Binary Inputs (Optical Couplers)

Function assignment and connections:

see address list (Appendix C) and terminal connection diagrams (Appendix E)

Fitted: 2 optical couplers, both freely configurable Nominal input voltage V_in,nom: 24 to 250 V DC

Binary Outputs (Output Relays)

Number, function assignment and connections: see address list (Appendix C) and terminal connection diagrams (Appendix E)

Fitted: 8 output relays, all freely configurable Contact load rating:

- Rated voltage: 250 V DC, 250 V AC - Continuous current: 5 A

- Short-time current: 30 A for 0.5 s

- Making capacity: 1000 W (VA) at L/R = 40 ms

- Breaking capacity: 0.2 A at 220 V DC, L/R = 40 ms, 4 A at 220 V AC, cos j = 0.4

2.6 Interfaces

Local control panel

Input and output of protection data: via six keys and two four-digit displays State and fault indications:

12 LED indicators

(3 permanently assigned, 9 freely configurable) Function assignment:

see address list (Appendix C) PC interface

Transmission rate:

300 to 9600 Baud (adjustable)

For connection to a PC, a special connection cable is required (see Accessories).

ILSA interface (optional) Per IEC 60870-5-103 Transmission rate:

50 to 19,200 Baud (adjustable) Plastic fiber connection

optical wave length: typ. 655 nm distance to be bridged: max. 45 m

Glass fiber connection G 50/125 or G 62.5/125 optical wave length: typ. 820 nm

2.7 Information Output

Counters, measured data and indications: see address list (Appendix C)

Time-Tagged Fault Logging

Up to 5 faults are stored, then the oldest fault is erased. Up to 64 signals per fault can be stored, subsequent signals trigger the overflow indication.

Fault counting: 0 to 9999.

Time-tagging: Date and time are assigned via an internal clock.

Fault Data Acquisition

Phase currents IA, IB, IC: to 100 Inom

(IN is calculated at output)

Phase-to-ground voltages VA-G, VB-G, VC-G: to 1 Vnom

(VN-G is calculated at output)

Resolution for sampled values ó 6% dynamic range: for Inom = 1 A : 6.1 mA (r.m.s.)

for Inom = 5 A, : 30.5 mA or 6.1 mV (r.m.s.)

Resolution for sampled values > 6% dynamic range for Inom = 1 A : 97.6 mA (r.m.s.)

for Inom = 5 A, : 488 mA or 97.6 mV (r.m.s.)

Time resolution: 2 ms Fault logging period

Pre-fault period: 10 to 100 ms Post-fault period: 10 to 250 ms

For a single fault, recording ceases after 4.35 s / 3.33 s (including the pre- and post-fault periods) at a nominal frequency of 50 Hz / 60 Hz.

The maximum recording period of 4.35 s / 3.33 s can be divided between up to 5 faults.

For a recording period in excess of 4.35 s / 3.33 s, the

2.9 Typical Characteristics

Min. starting time: 25 ms

Starting reset time: 30 ms ± 10 ms

Directional sensitivity up to 2 s after general start: ¥ beginning 2 s after general start and with switch on to fault: 200 mV ± 20%

Shortest command time: 35 ms

Minimum trip command output time: 100 ms Reset ratio for starting and measurement: 0.95

2.10 Deviations

Deviations relative to the set value with sinusoidal measured variables, total harmonic distortion £ 2%, ambient temperature 20°C and nominal auxiliary voltage V_A,nom.

Distance Protection

Fault detector I>, I_N>

Setting <0,2 I_nom: Deviation: ± 5% Setting >0,2 I_nom: Deviation: ± 3% Influence at 20°C ± 20 K: ± 0.5% Influence at f_nom ± 5%: ± 0.5% Fault detector I>>

Deviation: ± 3% Influence at 20°C ± 20 K: ± 0.5% Influence at f_nom ± 5%: ± 0.5% Fault detector V<, V_N-G>, V_N-G>> Deviation: ± 3% Influence at 20°C ± 20 K: ± 0.5% Influence at f_nom ± 5%: ± 2.0% Impedance measurement Z<

Backup Overcurrent Time Protection (Backup DTOC)

Threshold operate value I> Deviation: ± 3%

Influence at 20°C ± 20 K: ± 1% Influence at f_nom ± 5%: ± 0.2%

Ground Fault Direction Determination Using Steady-State Values

Threshold operate values and sector angles Deviation: ± 3% or 1 °

Influence at 20°C ± 20 K: ± 1% or 1° Influence at f_nom ± 5%: ± 5% or 2°

Measuring Circuit Monitoring

Threshold operate values I_neg, V_neg Deviation: ± 3%

Influence at 20°C ± 20 K: ± 1%

Timer stages

Deviation: ± 10 ms or 3% Influence at 20°C ± 20 K: ± 1%

Operating Data Measurement

Deviations relative to the relevant nominal value with sinusoidal measured variables, total harmonic distortion £ 2%, ambient temperature 20°C and nominal auxiliary voltage V_A,nom.

Current, voltage Deviation: ± 3%

Influence at 20°C ± 20 K: ± 1% Influence at f_nom ± 5%: ± 0.2% Active and reactive power Deviation: ± 11% Influence at 20°C ± 20 K: ± 7% Influence at f_nom ± 5%: ± 6% Load angle j Deviation: ± 2° Fault Localization Deviation: ± 5% Internal Clock

With free-running internal clock Deviation: < 1 min/month

With synchronization via DCF77 clock Deviation: < 10 ms

2.11 Power Supply

Nominal auxiliary voltage V_A,nom

24 to 60 V DC / 110 to 250 V DC, 100 to 230 V AC 1 (selectable using internal plug-in jumper)

Operating range: 0.8 to 1.1 V_A,nom with residual ripple of up to 12% V_A,nom f_nom: 50 Hz / 60 Hz 2

Nominal consumption at V_A,nom = 220 V DC: 8 / 10 W (VA) (initial condition / operated condition) Start-up peak current for a duration of 0.25 ms: < 13 A

3.1 Modular Structure

The PD 521, a numerical protection device, is one of the pieces of instrumentation in Subsystem P of the Integrated Protection and Control System for Substations (ILS). The devices that are part of this system are built from identical uniform hardware modules. Figure 1 shows the basic hardware structure of the PD 521 distance protection device.

1 Basic hardware structure

The input transformers and optical couplers convert the external analog and binary variables electrically isolated -to the internal processing levels. Commands and signals generated within the device are accessible via floating contacts. The external auxiliary voltage is applied to the power supply module which provides the voltages required internally.

3.2 Man-Machine Communication

The following interfaces are available for the exchange of information between operator and device:

¨ Integrated local control panel

¨ PC interface

¨ ILSA interface

Each piece of information and each parameter is coded with an ‘address’ consisting of two two-digit decimal numbers x and y. Changing x or y allows selection of any desired address for display or where necessary

modification of the information stored at that address. (Please refer to Chapter 6.)

The addresses are standardized for all systems with the advantage that the same information is coded with the same address in each device type. The entire address range is divided into the following three groups:

¨ Parameters:

This group contains all set values including the device identification data, the configuration parameters for adapting the device interfaces to the system and the function parameters for adapting the protective function to the process. All values of this group are stored in a non-volatile memory, that is the values will be

preserved even if the power supply fails.

¨ Operation:

This group includes all information relevant for operation, such as measured operating values and binary signal states. This information is updated periodically and consequently is not stored. In addition, various control parameters are grouped here, for example those for resetting counters, memories and displays.

¨ Events:

3.3 Distance Protection

The secondary phase currents and voltages of the system transformer are fed to the PD 521 and – electrically isolated – are converted to normalized electronics levels. The analog quantities are digitized and are thus available for further processing.

Settings that do not refer to nominal quantities are converted by the PD 521 to nominal quantities. The nominal current of the PD 521 must be set for this purpose.

The connection arrangement of the distance protection measuring circuit on the PD 521 must be set. (Figure 2 shows the standard connection.) The phase of the digitized phase current is rotated 180° by this setting.

From these currents (IA, IB and IC) the phase-to-phase

currents IA-B, IB-C and IC-A are formed.

The current with the highest magnitude (IP,max) and the

current with the intermediate magnitude (IP,med) are

determined from the phase currents.

The ground current 1IN is calculated by summation of IA, IB

and IC.

The phase-to-phase voltages 1VA-B, 1VB-C and 1VC-A are

formed from the digitized phase-to-ground voltages 1VA-G, 1VB-G and 1VC-G and the neutral displacement

3.3.1 Fault Detection Logic

The purpose of distance protection fault detection logic is phase-selective short-circuit detection. Fault detection logic is divided into the following areas:

¨ Overcurrent detection

¨ Ground fault detection

¨ Undervoltage detection

¨ Underimpedance detection

The fault detection decisions of the individual areas are linked by fault detection logic.

Short-circuit currents that are greater than the maximum operating load currents can be detected by overcurrent detection logic. Undervoltage detection logic is provided for short circuits that cannot be detected by overcurrent detection logic. Ground fault detection logic distinguishes between grounded and ungrounded faults.

The fault detection logic function starts the timer stages of the trigger levels and – as a function of the

phase-selective fault detection decision – selects the measuring loop in which the fault impedance is determined. Fault detection logic is blocked in the following cases:

¨ if protection is disabled from the local control panel or through appropriately configured binary signal inputs;

¨ if measuring-circuit monitoring detects a fault in the voltage-measuring circuit.

Protection can only be deactivated or activated through binary signal inputs if the M A I N : D e a c t i v a t e p r o t . E X T and M A I N : A c t i v a t e p r o t . E X T functions are both configured. When only one or neither of the two functions is configured, this is interpreted as “Protection externally activated.” If the triggering signals of the binary signal inputs are implausible, as for example when they both have a logic value of “1,” then the last plausible state remains stored in memory.

Overcurrent Detection Logic

Overcurrent detection logic monitors the phase currents for values in excess of the threshold values I>> and I>>>. The I>> threshold can be set. I>>> is 2× >>I . The thresholds are identical for all three phases.

The output signals of the I>> trigger assume a logic value of "1" if the threshold is exceeded in two consecutive half-waves. Overcurrent detection is delayed by the set time tI>> if the current is below 5 × I>>. Thereby, false fault

detection decisions caused by inrush currents on switching can be suppressed for lines with connected transformers. In the case of the I>>> trigger only one half-wave must exceed the threshold for the output signals to assume a logic value of "1."

If I>> is exceeded in one phase, then it is sufficient for overcurrent detection if I>>> is exceeded in the other phases. In this case the fault detection time is shortened since there is no longer any need to wait for the second half-wave.

Evaluation of the trigger decisions is a function of the type of neutral-point treatment set in the PD 521. If isolated-neutral/resonant-grounded or short-time grounding is set, then I>> overcurrent detection occurs in the phase(s) in which the I>> threshold is exceeded. With the setting impedance-grounded the following condition must also be satisfied:

I³ ×2 I_P

Ground fault detection logic monitors the average

magnitude of the ground current 1IN and the neutral-point

displacement voltage 1VN-G for values exceeding set

thresholds.

5% of the current maximum phase current is added to the set threshold IN>, which means that the operate value of

the ground current function increases with an increasing phase current level as a form of stabilization.

5 Monitoring the ground current 1IN and the neutral-point displacement voltage 1VN-G

The ground fault detection mode is a function of the neutral-point treatment set in the PD 521.

¨ M A I N : N e u t r a l - p o i n t t r e a t ( m e n t ) Low impedance-grounding

Ground fault starting SG occurs with this setting when

the threshold of the IN> or VN-G> trigger is exceeded.

¨ M A I N : N e u t r a l - p o i n t t r e a t ( m e n t ) Isolated neutral/resonant-grounding

If the setting isolated neutral/resonant-grounding is selected, instantaneous starting SG occurs when there

is multiple phase-to-ground fault detection if the threshold value of the IN> or VN-G> trigger is exceeded.

Even in the case of a single-phase fault, that is, in the event that only one base point is detected, ground fault starting will occur, but not until t_IN> has elapsed.

¨ M A I N : N e u t r a l - p o i n t t r e a t ( m e n t ) Short-duration grounding

Operation in this mode corresponds to operation with the setting isolated neutral/resonant-grounding except that timer stage tIN> is started when the IN> or VN-G>

trigger operates. In the case of a sustained ground fault the timer stage tIN> remains in the elapsed state

due to the operating trigger VN-G>>. If the ground fault

changes to a phase-to-ground fault then ground fault starting operates without delay when the threshold of the IN> or VN-G> trigger is exceeded.

Ground Fault Starting Signals

Signals are derived from ground fault detection trigger decisions. If neutral-point treatment is set for Low impedance-grounding, then the following signals are issued:

¨ When VN-G>> is exceeded,

S T A R T : V N - G > > t r i g g e r e d is signaled.

¨ By selecting the appropriate setting the user can specify whether a “trip” should occur after the timer stage tVN-G>> has elapsed.

With the settings Isolated neutral/resonant-grounding or Short-duration grounding the M A I N : G r o u n d f a u l t signal is issued after tVN-G>> elapses (see Figure 6) if there

is no multi-phase starting.

7 Ground fault starting signals

Enabling Undervoltage and Underimpedance Detection Logic

Undervoltage and underimpedance detection logic are enabled by I>(Imin) in the corresponding measuring

systems. In order to control contention problems when current and voltage appear at the same time (branch voltage transformers), enabling of the measuring systems is delayed by 15 ms.

In isolated-neutral systems or resonant-grounded systems, one of the two phases may carry just a small load current falling below the base point current I>(Imin).

In this case, the undervoltage decisions are enabled if the V< condition is met in two phases whereas the I>

condition is satisfied in one phase only. This extended enabling logic will operate only for the neutral-point treatment settings Isol./reson. w. start. P-G and Short-duration grounding.

Undervoltage Detection Logic

Undervoltage detection logic monitors the phase-to-ground voltages or the phase-to-phase voltages to determine whether they fall below the set threshold V<. Operation of undervoltage detection can be determined through selection of the operating mode. The following modes are possible:

¨ Undervoltage detection logic is deactivated.

¨ Undervoltage detection logic evaluates only the

decisions of the phase-to-ground loops, once these functions have been enabled by ground fault detection.

¨ Ground fault detection brings about a switch from phase-to-phase to phase-to-ground loops.

If the following – contradictory – setting combination has been selected, namely

¨ M A I N : N e u t r a l - p o i n t t r e a t ( m e n t ) Isol./reson. w/o start P-G and

¨ S T A R T : O p e r a t ( i n g ) m o d e With V</Z< starting P-G,

then when ground starting SG occurs, the phase-to-phase

loops are always enabled. If no ground starting occurs, then the undervoltage detection function is blocked.

Underimpedance Detection Logic

Underimpedance detection logic determines the impedances of the phase-to-ground or phase-to-phase loops.

Operation of underimpedance detection logic – as well as undervoltage detection logic – can be controlled through selection of the operating mode. The following modes are possible:

¨ Both the underimpedance and undervoltage detection

logic are disabled.

¨ The underimpedance and undervoltage detection functions evaluate only the decisions of the phase-to-ground loops, once these functions have been enabled by ground fault detection logic.

¨ Ground fault detection brings about a switch from phase-to-phase to phase-to-ground loops.

If, as a special case, the following – contradictory –setting combination has been selected, namely

¨ M A I N : N e u t r a l - p o i n t t r e a t ( m e n t )

"Isol./reson. w/o start P-G" and

¨ S T A R T : O p e r a t ( i n g ) m o d e “With V</Z< starting P-G",

then when ground starting SG occurs, the phase-to-phase

loops are always enabled. If no ground starting occurs, then the undervoltage and underimpedance detection functions are blocked.

All underimpedance detection measuring loops are blocked when the trigger I>>> operates (see ‘Overcurrent detection logic’). When overcurrent or undervoltage detection logic operates, the corresponding measuring loops are blocked phase-selectively.

If measurement is enabled, the loop impedance is

The following values must be set in order to determine the underimpedance detection characteristic:

¨ Reactance in the forward direction: X_fw

¨ Load angle >

¨ Ratio Z_bw/Z_fw

(Impedance in backward direction: Z_bw Impedance in forward direction: Z_fw)

¨ Phase-to-ground resistance in forward direction:

R_fw P-G

¨ Phase-to-phase resistance in forward direction: R_fw P-P

If, on the basis of the settings, the reach in the backward direction is greater than 3× Znom, then the range is limited to 3× Znom (

Z

=

V

/

I

Fault Detection Logic

The fault detection logic links the phase-selective output signals from

¨ Overcurrent detection logic (I>>)

¨ Ground fault detection logic

¨ Undervoltage detection logic (V<)

¨ Underimpedance detection logic (Z<)

to form common phase-selective starting decisions SA, SB,

SC and SN1. The decisions SA, SB and SC are combined to

form "distance protection starting" – and thus the

S T A R T : G e n e r a l s t a r t i n g signal. Ground starting alone does not bring about general starting.

In the case of starting via overcurrent detection logic, single-phase starting without ground may occur. In order for the measured values for distance and directional measurement to be properly selected even in this case, either SN1 starting or starting in another phase must be

triggered as well. It is possible to specify whether in the case of single-phase starting, SN1 starting will always be

tripped or whether – depending on the magnitude of the phase currents – SN1 or starting in one phase shall be

transfer-tripped.

¨ M A I N : T r a n s f e r f o r 1 p Ground

With single-phase overcurrent detection logic, SN1 is

started and transfer-tripped after the timer stage tIN>

has elapsed (see "ground fault detection logic" for setting).

If starting changes from single-phase overcurrent starting without ground to multi-phase starting or single-phase-to-ground starting, starting occurs instantaneously.

¨ M A I N : T r a n s f e r f o r 1 p P or G = f(I_P,med , I_P,max)

The decision as to whether starting in one phase or SN1 starting will be tripped is derived from the ratio

I_{P med,} / I_P,max . The magnitude of the medium phase current must be more than 2/3 the magnitude of the maximum current so that the phase is transfer-tripped. If the current with the medium-sized magnitude is smaller, SN1 will be tripped after the timer stage tIN>

has elapsed.

If starting switches from single-phase overcurrent starting without ground to multi-phase starting or single-phase-to-ground starting, starting will be instantaneous.

3.3.2 Selection of Measured Variables

The PD 521 selects a measuring loop based on the phase-selective fault detection decision and the selected phase priority. The short-circuit impedance and fault direction are determined from this measuring loop’s voltage and current.

In the case of three-phase fault detection, either grounded or ungrounded, the minimum voltage of the phase-to-phase voltages and the associated phase-to-phase-to-phase-to-phase current are selected as measured variables. In the case of double-phase-to-ground fault detection, the set phase priority is the determining factor for selecting the

3.3.3 Distance and Directional Measurement

The PD 521 determines the fault impedance and the fault direction on the basis of the selected measured variables. A voltage memory is available so that measurement will function correctly, even with very low fault voltages.

Voltage Memory

The voltage 1VA-B is the reference voltage for the voltage

memory. If the voltage exceeds the default value of 0.65 Vnom and if there is no "distance protection starting,"

then the voltage memory is synchronized.

Synchronization requires approximately 100 ms. Then a check is carried out to determine whether the frequency satisfies the following condition:

0 99. ×fnom < <f 101. ×fnom.

If the condition is satisfied, the voltage memory is enabled. The frequency condition is checked in cycles at intervals of approximately 10 ms. As soon as the condition is no longer satisfied, the enable is canceled.

If the magnitude of the reference voltage drops below 0.65 Vnom or if “distance protection starting” occurs,

synchronization of the voltage memory is terminated. The voltage memory is then free-running and remains enabled for 2 s.

Angle Determination

When "distance protection starting" occurs, the angles jF

and jS are determined.

Angle jF is the fault angle that is determined using the

selected measuring voltage Vmeas and the selected

measuring current Imeas. In order for the fault angle jF to

also be reliably determined in the event of arcing faults, only the fundamental wave of the measuring voltage is used for angle measurement.

Angle jS is determined on the basis of the voltage stored

in memory and the selected measuring current Imeas.

Since the frequency of the stored voltage can differ from the nominal frequency, a phase correction must be made. This correction is determined by the frequency deviation and the time that has elapsed since synchronization was terminated. Furthermore, an angle correction as a function of the selected measuring loop and the M A I N : R o t a r y f i e l d setting is necessary. The resulting angle jX is used for further processing.

For distance and directional measurement the following angles are used – as a function of the magnitude of the selected measuring voltage and the fault duration:

¨ the fault angle jF,

¨ the angle jX,

¨ the set angle a.

Directional Measurement

If the selected measuring voltage Vmeas is greater than

0.15 Vnom when the fault occurs, then the direction is

determined using the fault angle jF. In the case of a

measuring voltage of less than 0.15 Vnom, the

angle jX is used for directional determination. If the

voltage memory is not enabled, the angle jX cannot be

determined. In this case a check is made to determine whether the measuring voltage Vmeas is in the range

200 mV < Vmeas < 0.15 Vnom. If this is not the case,

direction is determined using the fault angle jF.

Directional determination using jX or jF is not possible if

the voltage memory is not enabled or if the measuring voltage is less than 200 mV. In these cases the set angle a is used for directional measurement, which means that a decision is made in favor of the forward direction.

Angle for Directional Determination

V. memory 0 002. ×Vnom<Vmeas<0 15. ×Vnom Vmeas<0 002. ×Vnom

Enabled _j

X jX

Not enabled _j

F a

A decision is made for forward direction if the angle selected for directional determination is in the range - °< < +45 j 135°. In the case of angles outside this range a decision is made for the backward direction.

Distance Measurement

For distance measurement, the user may select a polygonal or circular characteristic by way of the setting DIST: Characteristic.

18 Selecting the characteristic

The angle that is used to calculate fault impedance is selected according to the following criteria:

¨ If the measuring voltage Vmeas is greater than 0.15 Vnom

when the fault occurs, then fault angle jF is used to

calculate fault impedance.

¨ If the fault voltages are less than 0.15 Vnom and the

voltage memory is enabled, a check is made to determine whether angles jF and jX are in the forward

direction (-45° < j < +135°).

n If both angles are in the same direction, either forward or backward, then fault angle jF is selected

for distance measurement.

n If angle jF is in the forward direction and angle jX is

in the backward direction, then an angle of 180° + a is specified for the calculation.

n If angle jX is in the forward direction and angle jF is

in the backward direction, the set angle a is used for distance measurement.

¨ If the voltage memory is not enabled, a check is made to determine

n whether the measuring voltage Vmeas is in the range

200 mV < Vmeas < 0.15 Vnom. If so, fault angle jF is

selected for the impedance calculation;

n whether the selected measuring voltage Vmeas is

less than 200 mV. If so, the set angle a is used for the impedance calculation.

The angle a can be set separately for the ‘polygon’ and ‘circle’ characteristics.

DIST : Characteristic “Polygon“

The fault impedance value ZF is determined using the

selected measuring quantities Vmeas and Imeas. By

multiplication by the cosine or sine of the angle selected for distance measurement jZ, we then calculate the fault

resistance RF or fault reactance XF.

20 Impedance measurement with the polygonal characteristic

The calculated quantities RF and XF are compared with the

reference quantities Rref and Xref of the four impedance

zones. The reference quantities are determined using the settings for determining the impedance zone(s). If both quantities lie within the set impedance zone(s), a distance decision is made for the corresponding zone(s).

The impedance zones are determined by the following settings:

¨ Reactance X

¨ Resistance R, separately for phase-to-ground and phase-to-phase loops

¨ Angle a

Using these settings in the R-X diagram we obtain the characteristic shown in Figure 21.

21 PD 521 impedance and directional characteristics for the setting “Polygon“

Example for: Xn = 6.5 ₉ Rn = 2.0 ₉ =n = 70° n = 1 to 4 Dot-dash line: k_ze = 1.2

The resistances for phase-to-ground and phase-to-phase loops can be set separately for each zone. The different impedances are therefore compared with different impedance characteristics.

In addition to the settings described above, the zone extension factors kze can be set separately for

phase-to-ground (P-G) and phase-to-phase (P-P) loops for impedance zone 1.

As a result of this setting, impedance zone 1 is extended or reduced accordingly in the R and X directions. Thus the R and X values modified by the zone extension factor kze are calculated according to the following

formulas: R_1,kze =k_ze×R₁

X_1,kze =k_ze×X₁

If, as a consequence of the settings kze, a wider reach

than 200 W at Inom = 1A or 40 W at Inom = 5 A results in R- or X-direction, then the reach is automatically limited to 200 W or 40 W, respectively.

The increase in reach by the zone extension factor kze HSR is controlled by

¨ protective signaling (PSIG: Z o n e e x t . );

¨ switch on to fault protection

(S O T F : Z o n e e x t e n s i o n );

¨ an external signal

DIST : Characteristic “Circle“

The fault impedance value ZF is determined using the

selected measuring quantities Vmeas and Imeas. If the setting

“Arc compensation: yes “ has been chosen then, for angles of - °<45 jZ <a and 135°<jZ <(a+180°) , a correction to the measured fault impedance is calculated as follows: Z_{F corr,} ZF sin = + 1 @

In the range - °<45 jZ <a the following relation holds: d a j= - Z

In the range 135°<jZ <(a+180°) we have: d a j= - Z +180°

The calculated impedance Z_meas is compared with the set impedance in the four impedance zones. If the measured impedance is smaller than or equal to the set impedance, then a distance decision of the corresponding zone(s) is taken.

In the R-X diagram, the characteristic shown in Figure 24 is obtained. If the characteristic were to be measured with sine variables for the setting “Arc compensation: yes", the dot-dashed line would be obtained.

24 PD 521 impedance and directional characteristics for the setting “Circle“

Example for: n = 1 to 4 = = 60°

Nfw = forward direction

Nbw = backward direction

Dot-dash line: with arc compensation

26 Setting impedance zones 2 to 4 and distance measurement

In addition to the settings described above, the zone extension factors kze can be set separately for

phase-to-ground (P-G) and phase-to-phase (P-P) loops for

impedance zone 1. The impedances modified by the zone extension factor kze are calculated as follows:

Z_1,kze =k_ze×Z₁

The increase in reach by the zone extension factor kze HSR is controlled by

¨ protective signaling (PSIG: Z o n e e x t . );

¨ switch on to fault protection (S O T F : Z o n e e x t e n s i o n );

¨ an external signal

3.3.4 Impedance-Time Characteristics

A maximum of four impedance zones and six timer stages are available for impedance time grading. All impedance zones can be operated in a forward direction, backward direction, or non-directionally. The distance-independent timer stage t5 can also operate forward-directionally, backward-directionally or non-directionally. Timer stage t6 operates independently of distance and direction. All timer stages are started by "distance protection starting." The stage times are corrected by the inherent delay or operate time of starting (approximately 30 ms).

Zone 4 can be utilized as a special zone by means of the D I S T : Z o n e 4 setting. This makes it possible to implement special characteristics for applications in cable or line networks.

When the D I S T : Z o n e 4 setting is "Normal", the impedance zones, timer stages and directional settings are assigned as follows:

Impedance zone 1 Direction N1 t1

Impedance zone 2 Direction N2 t2

Impedance zone 3 Direction N3 t3

Impedance zone 4 Direction N4 t4

Direction N5 t5

t6

The "Distance trip" decision is reached for zones 1 to 4 if the following criteria are satisfied simultaneously:

¨ A distance decision exists for the zone.

¨ The timer stage assigned to this impedance zone has elapsed.

¨ The measured direction agrees with the directional setting assigned to this impedance zone.

If several timer stages and directions are set to the same values, a distance trip occurs in the zone with the highest number.

The "Distance trip zone 5" decision is reached if the following conditions are satisfied simultaneously:

¨ Timer stage t5 has elapsed.

¨ The measured direction agrees with the directional setting for N5.

After timer stage t6 has elapsed, the "Distance trip zone 6" decision is reached.

If protective signaling (PSIG) is used in the operating modes Signal comparison blocking scheme or Signal comparison pilot wire, a distance trip occurs instanta-neously in zone 1 if the following conditions are satisfied simultaneously:

¨ There is a distance decision in zone 1.

¨ The measured direction agrees with the directional setting for N1.

Special Zones

¨ D I S T : Z o n e 4 "Section cable-line"

This setting is selected for a mixed cable-line section if automatic reclosing will only be carried out if there is a fault in the line area. In this case the cable must form the front part of the transmission section and the line the rear part.

Timer stage t1 and the N1 directional setting are assigned to impedance zones 1 and 4. The setting for timer stage t4 and the N4 directional setting are inactive.

The "Distance trip Zone 1" or "Distance trip Zone 4" decision is reached if the following conditions are satisfied:

n A distance decision for zone 1 or zone 4 exists.

n The measured direction agrees with the direction set for N1.

n Timer stage t1 has elapsed.

In order for the PD 521 to determine the section in which the fault is located, impedance zone 1 must be set for the total length of the transmission section and impedance zone 4 for the length of the cable. If a distance trip for zones 1 and 4 occurs after t1 has elapsed, then the signal DIST: Fault in cable run is generated.

¨ D I S T : Z o n e 4 "Section line-cable"

This setting is selected in the case of a mixed line-cable section if automatic reclosing will only be carried out if there is a fault in the line area. In this case the line must form the front part of the transmission section and the cable the rear part.

Timer stage t1 and directional setting N1 are assigned to impedance zones 1 and 4. The setting for timer stage t4 and directional setting N4 are inactive. The "Distance trip zone 1" or "Distance trip zone 4" decision is reached if the following conditions are satisfied:

n A distance decision for zone 1 or zone 4 exists. n The measured direction agrees with the direction

set for N1.

n Timer stage t1 has elapsed.

In order for the PD 521 to determine the section in which the fault is located, impedance zone 1 must be set for the total length of the transmission section and impedance zone 4 for the length of the line. If a distance trip only occurs in zone 1 after t1 has elapsed, then the signal DIST: Fault in cable run is generated.

3.4 Measuring-Circuit Monitoring

The PD 521 monitors the phase currents and voltages for balance during healthy system operation. If unbalance or the lack of measuring voltage is detected, action is taken to prevent the protection device from malfunctioning. The monitoring signals issued in the event of a fault in the measuring circuits are entered in the monitoring signal memory. If this is not desired, entry of the monitoring signals in the monitoring signal memory can be disabled.

Ground starting results in a warning signal if at least one phase-to-ground voltage is greater than 0.7 Vnom/Ö3.

Thereby, warnings for lines disconnected at both ends are avoided in low-impedance-grounded systems where capacitively coupled neutral-displacement voltages in excess of VNG> may occur.

Measuring circuit monitoring can be deactivated by the appropriate setting. In the event of a fault, measuring circuit monitoring is blocked.

Monitoring the Current-Measuring Circuits

The current-measuring circuit monitoring function is enabled when the current exceeds the value 0 125. × Inom in at least one phase. Once monitoring is enabled, the absolute value of the negative-sequence component of the current system is determined in accordance with the definition of the Symmetrical Components.

This value is divided by the maximum phase current I_P,max and compared to the set threshold operate value. If the set threshold operate value is exceeded, a

monitoring signal is issued after 10.1 s. In addition, a setting can be selected that will determine whether a trip shall occur.

Monitoring the Voltage-Measuring Circuits

The voltages used by distance protection as measured variables are monitored by the voltage-measuring circuit monitoring function for plausibility. However, this does not replace the auxiliary contact of the voltage transformer m.c.b., which is absolutely necessary in the case of activated undervoltage and underimpedance starting. Monitoring of the voltage-measuring circuits is based on the following criteria:

¨ Monitoring the phase-to-phase voltages for voltages that fall below the default threshold of 0 4. ×Vnom. This monitoring function is enabled when the phase current is greater than 0 05. × Inom or for the “closed“ position of the circuit breaker provided that MON: Meas. volt. circuit is set to Vneg w. CB contact enabl.

¨ Monitoring the negative-sequence component of phase-to-ground voltages in accordance with the definition of the symmetrical components. Monitoring is enabled when a phase-to-ground voltage exceeds the default threshold of 0 7. ×Vnom / 3. In addition to this criterion, a minimum current having the default threshold setting of I>0 05. ×Inom or the closed position of the circuit breaker can be used as enabling criteria. If there is an enable, the absolute value of the

negative-sequence component of the voltage system is determined in accordance with the definition of

symmetrical components.

This value is compared with the default threshold operate value 0 2. ×Vnom / 3. If the threshold operate value is exceeded, a monitoring signal is issued after

If one of the monitoring functions described above operates, then distance protection is blocked and the device switches to backup overcurrent time protection – if the appropriate setting was selected.

In addition, the monitoring signal “M O N : M e a s . v o l t . O K ” is issued if all phase-to-phase voltages exceed the default threshold of 0 65. ×Vnom and negative-sequence monitoring has not operated.

Monitoring Starting

If ground starting S_G is present for more than 10 s without phase starting, the following monitoring signal is issued: M O N : M e a s u r i n g c i r c u i t s "Ground fault starting" (see Figure 35).

3.5 Backup Overcurrent-Time Protection (BUOC or Backup DTOC)

If there is a fault in the voltage-measuring circuit, distance protection is blocked, since accurate impedance

measurement is not possible. Backup overcurrent time protection is automatically activated – if set accordingly. Backup overcurrent time protection is enabled if there is a fault in the voltage-measuring circuit. It monitors the phase currents for overcurrents exceeding the set values I>. If a phase current exceeds the set value, timer stage

t_I> is started. After the set time period has elapsed, a trip signal is issued.

If the "Low impedance-grounding" setting has been selected, the ground current 1I_N is also monitored by the settable trigger I_N>, in addition to the phase currents. If the ground current exceeds the set value, timer stage t_IN> is started. After the set time has elapsed, a trip signal is issued.

3.6 Switch on to Fault Protection

When the circuit breaker is closed manually it is possible to switch on to an existing fault. This is especially critical if the line in the remote station is grounded since the

distance protection would not clear the fault until t2 had elapsed. The fastest possible clearance is desirable in this situation, however.

To guarantee rapid clearing with manual closing, the manual close signal must be issued not only to the circuit breaker but also to the PD 521. The manual close signal

is converted to an internal pulse. The pulse time can be set. It is possible to specify whether the following shall occur during operation of the timer stage:

¨ The appearance of general starting (see Section “Tripping Logic” for a definition of general starting) shall cause a trip (S O T F : T r i p a f t . m a n . c l o s e ). or

¨ A zone extension of impedance zone 1 shall occur (SOTF: Zone extension).

3.7 Protective Signaling

The reach of the first impedance zone of the distance protection function is normally set for values less than 100%. Protective signaling is used to extend protection to 100% of the section. This is achieved by logical linking of the signals that are transmitted by the remote station’s protection device.

In order for protective signaling (PSIG) to function, the following requirements must be satisfied:

¨ It must be activated.

¨ There must be no external block.

¨ There must be no transmission fault.

¨ The function PSIG: Receive EXT must be configured to a binary signal input.

Protective signaling can be activated or deactivated from the local control panel.

Once protective signaling is ready, distance protection timer stage t1 is blocked. A trip enable in distance protection zone 1 is then issued after the protective signaling tripping time has elapsed.

41 Protective signaling tripping time

A communication malfunction or failure leads to a

protective signaling block. If protective signaling is carried out by a signal transmission or communication device, the device’s fault signal can be connected. In the case of protective signaling via pilot wires or in the operating mode referred to as "reverse interlocking," an internal monitoring function detects any fault in the communication channel. Protective signaling can be operated in seven different modes. The following operating modes require a signal transmission device:

¨ Direct transfer trip underreaching

¨ Permissive underreaching transfer tripping (PUTT)

¨ Zone extension

¨ Signal comparison release scheme

¨ Signal comparison blocking scheme

For operation in the mode referred to as "Signal compari-son pilot wire," pilot wires are required for signal trans-mission.

P S I G : O p e r a t i n g m o d e "Direct transfer trip underreaching"

When there is a “Distance trip zone 1" a signal is sent to the remote station’s protection device. Upon receipt of the signal by the remote station, the remote station’s circuit breaker is tripped.

P S I G : O p e r a t i n g m o d e "Permissive underreaching transfer tripping (PUTT)”

With a "Distance trip zone 1" a signal is sent to the remote station’s protection device. Upon receipt of the signal by the remote station, the remote station’s circuit breaker is transfer tripped as a function of starting.

P S I G : O p e r a t i n g m o d e "Zone extension"

With "Distance trip zone 1" a signal is sent to the remote station’s protection device. Upon receipt of the

transmitted signal the measuring range of zone 1 in the remote station is increased by the zone extension factor k_ze HSR. If the fault lies within the extended zone, the remote station’s protection device also decides in favor of “Distance trip zone 1.”

43 Reaches with zone extension

(broken line: measuring range increased by the zone extension factor k_ze HSR)

P S I G : O p e r a t i n g m o d e “Signal comparison release scheme"

In the idle state the measuring range of zone 1 in both protection devices is extended by the zone extension factor k_ze HSR. The “Distance trip zone 1” of both protection devices is blocked.

If distance protection starting begins and the fault lies in the forward direction, a signal is sent to the remote station. In the event of a fault, both protection devices measure by using the normal measuring range and the range

extended by the zone extension factor k_ze HSR. A trip enable is issued if one of the following conditions is satisfied after the distance protection timer stage t1 has elapsed:

44 Zone reaches with the release scheme

(broken line: measuring range extended by the zone extension factor k_ze HSR)

If both zone extension factors (k_ze P-G HSR and k_ze P-P HSR) are set at a value of "1.0," a trip enable is issued only if the second of the conditions given above is satisfied.

In the event of a change in direction the received signal is ignored for 80 ms (“transient blocking”) so that false tripping will not occur in double line protection.

P S I G : O p e r a t i n g m o d e "Signal comparison blocking scheme"

In the idle state the measuring range of zone 1 in both protection devices is extended by the zone extension factor k_ze HSR. The “Distance trip zone 1” of both protection devices is enabled.

If distance protection starting begins and the fault lies in the backward direction, a signal is sent to the remote station.

In the event of a fault, both protection devices measure by using the normal measuring range and the range

extended by the zone extension factor k_ze HSR. A “Distance trip zone 1” can be issued instantaneously (t0)

45 Zone reaches with the blocking scheme

(broken line: measuring range extended by the zone extension factor k_ze HSR)

If both zone extension factors (k_ze P-G HSR and k_ze P-P HSR) are set at a value of "1.0," a trip is only possible after t1 has elapsed.

P S I G : O p e r a t i n g m o d e "Signal comparison pilot wire"

To form the communication link it is necessary to connect either the break contact or the make contact of the transmitting relay, depending on the transmitting relay mode selected (Transm. relay make contact or Transm. relay break contact), to the P S I G : R e c e i v e E X T input of the remote station by means of pilot wires. In the idle state there is a received signal in both protection devices (DC loop closed), and the measuring range of zone 1 is extended by the zone extension factor

k_ze HSR. The “Distance trip zone 1” of both protection devices is enabled.

If distance protection starting begins and a fault lies in the backward direction or if the overcurrent starting originates from the distance protection starting, then a signal is sent to the remote station without delay.

In the event of a fault both protection devices measure by using the normal measuring range and the measuring range extended by the zone extension factor k_ze HSR. A “Distance trip zone 1” can be issued instantaneously (t0) with the normal reach. The “Distance trip zone 1” is blocked if the following conditions are satisfied simultane-ously after distance protection timer stage t1 has elapsed:

¨ The fault lies within the extended measuring range.

¨ A transmitted signal is received by the remote station. If both zone extension factors (k_ze P-G HSR and

k_ze P-P HSR) are set at a value of "1.0," a trip is only possible after t1 has elapsed.

The pilot wires are monitored for interruptions. If, during fault-free operation, that is, when there is no distance protection starting, no signal is received by the remote station for a period longer than the set transmitted signal reset time plus 600 ms, then a P S I G : T e l e c o m . f a u l t y signal (see Figure 42) is issued, and protective signaling is blocked.

P S I G : O p e r a t i n g m o d e "Reverse interlocking"

In radial networks with infeed from a single end it is possible under certain conditions for busbar protection to be configured by sampling the starting of feeder protection devices. By means of appropriate interconnection, a send signal is then formed when a feeder protection device starts. The receipt of this signal by the PD 521 blocks the “Distance trip zone 1.” The blocking signal reset is delayed by approximately 80 ms.

The pilot wires are monitored. If a received signal is present for more than 10 s without any distance protection starting, then the distance trip zone 1 block is canceled. A new block cannot occur until the received signal has dropped out.

47 Reverse interlocking

Echo Function

It is possible to select "without or with" echo on receive. This setting is only active in the following modes:

¨ PUTT (permissive underreaching transfer trip)

¨ Zone extension

¨ Signal comparison release scheme

¨ Signal comparison blocking scheme

If the "with" echo setting is selected, a signal is sent to the remote station if the received signal is present for more than 50 ms and no “distance protection starting” is active.

The further transmission of a received signal as a send signal is then blocked for 20 s. This prevents a

permanent signal from being transmitted.

Testing the Communication Channel

The communication link can be tested. For this purpose a 500 ms send signal is issued through a binary signal input or the integrated local control panel. The remote station receives this signal if the transmission section is OK. In the mode referred to as "Direct transfer trip underreach" no test is possible, since a received signal will immediately lead to a “Trip” in the remote station. Likewise, testing is not possible with the "Reverse interlocking" setting.

3.8 Circuit Breaker Failure Protection

Circuit breaker failure protection is activated by a general trip command from the PD 521 or – when a general starting state exists – through an appropriately configured binary signal input. After the settable time period

C B F : t C B F has elapsed, the fault must be cleared. Otherwise it can be assumed that the circuit breaker has failed. In this case the C B F : C B f a i l u r e signal is issued.

53 Circuit breaker failure protection

3.9 Ground Fault Direction Determination Using Steady-State Values

Ground fault direction determination using steady-state values requires the neutralpoint displacement voltage -formed from the three phase-to-ground voltages - and the ground current as measured variables. A special

transformer is provided in the PD 521 for the residual current. The current transformer is designed specifically for this application so that it has a low phase-angle error. When there is a trip of the voltage transformer circuit breaker, ground faults can be determined by steady-state evaluation of the ground current. The user can specify whether both ground current and displacement voltage will be evaluated (steady-state power) or if only the ground current will be evaluated (steady-state current). The switch from steady-state power evaluation to steady-state current evaluation can also be carried out through a binary signal input – given appropriate configuration.

When switching from steady-state power to steady-state current evaluation or vice versa, the outputs of the non-active function are blocked.

If the system frequency is set to 60 Hz, ground fault direction determination using steady-state values (GFDSS) is blocked.

3.9.1 Steady-State Power Evaluation

In order to detect the ground fault direction, ground fault direction determination by steady-state power evaluation

requires the neutral-point displacement voltage 1V_N-G and the ground current 2I_N.