Programming Settings for Time-Overcurrent Phase Protection

General The functions associated with time-overcurrent protection were established during configuration of protective functions (Section 5.1) at address &KDUDF3KDVH. If address  was set to 'HILQLWH7LPHRQO\, then only the settings for the def-inite-time elements are available.

At address )&7, phase time-overcurrent protection may be switched 21 or 2)).

50-2 Relay Element The pickup and delay of the 50-2 relay element are set at addresses 

3,&.83 and '(/$< respectively. The 50-2 relay element is typically uti-lized for protection against high magnitude faults. For this reason, the relay element pickup is often set high while the delay is set short. It is always important to set the

T_50-1 T_50-2 t₁

T_50-1 T_50-2

t₁

TRIP TRIP TRIP TRIP

Fault Location B: Source-side Trip Time = T_50-2 = Source side 50-2 Delay Fault Location A: Load-side Trip Time = t₁

Source-side Backup Trip Time = T_50-1 =Source-side 50-1 Delay B

A Normal Load Flow

´%ORFN´

t₁

52

52 52

50-1 50-2 50-1 50-1

pickup and delay such that operation of the 50-2 element will coordinate with other protective equipment in the system.

Below is an example of how a 50-2 relay element might be set to protect a power transformer in a radial distribution system against high magnitude internal faults:

Example: Transformer used to supply distribution bus with the following data:

Based on the data above, the following are calculated:

The minimum pickup setting for the 50-2 element can be governed by a single inequal-ity:

If the pickup of the 2 relay element is set according to the inequality above, the 50-2 element will never pickup for a fault beyond the transformer’s low-side bushings, even if changing system conditions increase the high side fault MVA. Using the ine-quality above as a guide, a setting of 10.00 amperes is chosen for the 50-2 element.

At address , a short time delay should be entered to prevent inrush currents from initiating false trips.

For motor protection, the 50-2 relay element must be set smaller than the smallest phase-to-phase fault current and larger than the largest motor starting current. Since the maximum motor starting current is generally on the order of 1.6 times the nominal motor current, the 50-2 phase element should be set as follows:

The potential increase in starting current caused by overvoltage conditions is already

Base Transformer Rating 16 MVA

Transformer Impedance (Z_TX) 10 %

Nominal High Side Voltage 110 kV

Nominal Low Side Voltage 20 kV

Transformer Connection Delta-Grounded Wye

High Side Fault MVA 1,000 MVA

High Side Current Transformer Ratio 100 A / 1 A Low Side Current Transformer Ratio 500 A / 1 A

Three-phase high side fault current @ 110kV 5250 A Three-phase low side fault current @ 20kV 3928 A Three-phase low side fault current @ 110kV 714 A Transformer full load current @ 110kV

(IBase-110kV )

84 A Transformer full load current @20kV

(I_Base-20kV )

462 A High side current transformer ratio (CTR-HS) 100 A / 1 A Low side current transformer ratio (CTR-LS) 500 A / 1 A

50-2 Pickup 1

bus feeder breakers. The 50-1 element or 51 element will serve as redundant protec-tion for the bus. The pickup values of both the 50-2 unit and the 50-1 or 51 unit are set equal to each other. The time delay associated with the 50-1 or 51 element is then time-coordinated with the individual bus feeder devices.

The delay set at address  is in addition to the 50-2 pickup time. The delay of the 50-2 element may be set to ∞. The 50-2 element will then pickup and generate a mes-sage, but will never trip. If the 50-2 element is not required at all, then the pickup value should be set to ∞, thus preventing pickup, trip, and the generation of a message.

50-1 Relay Element The pickup value of the 50-1 relay element (set at address 3,&.83) should be set above the maximum anticipated load current. Pickup due to overload should never occur since the 50-1 relay element is designed only for fault protection.

For this reason, a setting equal to 120 % of the expected peak load is recommended for line protection, and a setting equal to 140 % of the expected peak load is recom-mended for transformers and motors.

If the 7SJ62 relay is used to protect transformers with large inrush currents, the ener-gization stabilization feature may be used to prevent a false trip of the 50-1 relay ele-ment. The configuration data for the inrush restraint feature is programmed at address block 22 (see Subsection 6.5.2).

The delay of the 50-1 element is set at address '(/$< and should be based on system coordination requirements.

The delay set at address  is in addition to the 50-1 element’s pickup time. The delay of the 50-1 element may be set to ∞. The 50-1 element will then pickup and gen-erate a message, but will never trip. If the 50-1 element is not required at all, then the pickup value should be set to ∞, thus preventing pickup, trip, and the generation of a message.

51 Relay Element With IEC Curves

Pickup of the 51 relay element will occur for currents greater than or equal to 110 % of the 51 element’s pickup value, and may or may not occur for currents between 100 % and 110 % of the 51 element’s pickup value. Dropout of the 51 relay element occurs when the current decreases to 95 % of the 51 element’s pickup value.

The pickup of the 51 element is set at address 3,&.83. As is the case for the 50-1 relay element, the pickup value of the 51 relay element should be set above the maximum anticipated load current. Pickup due to overload should never occur since the 51 relay element is designed only for fault protection. For this reason, a set-ting equal to 120 % of the expected peak load is recommended for line protection, and a setting equal to 140 % of the expected peak load is recommended for transformers and motors.

The 51 element time multiplication factor is set at address  7,0(',$/ and should be based on system coordination requirements.

The time multiplication factor may be set to ∞. The 51 element will then pickup and generate a message, but will never trip. If the 51 element is not required at all, address 0112 should set to 'HILQLWH7LPHRQO\ during protective function configuration (see Section 5.1).

51 Relay Element With ANSI Curves

Pickup of the 51 relay element will occur for currents greater than or equal to 110 % of the 51 element’s pickup value, and may or may not occur for currents between 100 % and 110 % of the 51 element’s pickup value. Dropout of the 51 relay element occurs when the current decreases to 95 % of the 51 element’s pickup value. If 'LVN

(PXODWLRQ is selected at address  'URSRXW, then reset occurs according to the reset curve as described in Subsection 6.2.1.2.

The pickup of the 51 element is set at address 3,&.83. As is the case for the 50-1 relay element, the pickup value of the 51 relay element should be set above the maximum anticipated load current. Pickup due to overload should never occur since the 51 relay element is designed only for fault protection. For this reason, a set-ting equal to 120 % of the expected peak load is recommended for line protection, and a setting equal to 140 % of the expected peak load is recommended for transformers and motors.

The corresponding time dial is set at address 7,0(',$/ and should be based on system coordination requirements.

The time dial may be set to ∞. The 51 element will then pickup and generate a mes-sage, but will never trip. If the 51 element is not required at all, address  should set to 'HILQLWH7LPHRQO\ during protective function configuration (see Section 5.1).

Manual Close Mode When a circuit breaker is closed into a faulted line, a high speed trip by the circuit breaker is often desired. The manual closing feature is designed to remove the delay from one of the time-overcurrent elements when a circuit breaker is manually closed into a fault. The time delay may be bypassed for one of the three time-overcurrent phase elements and one of the three time-overcurrent ground elements via an impulse from the external control switch, thus resulting in high speed tripping. This impuls is prolonged by a period of 300 ms. Address 0$18$/&/26( can be set such that the delay is defeated for the 50-2 element, the 50-1 element, the 51 element, or none of the elements (,QDFWLYH). Defeating the delay on just one of the three elements allows control over what level of fault current is required to initiate high speed tripping of a circuit breaker that is closed into a fault.

External control switch

If the manual closing signal is not from a 7SJ62, that is, neither via the built-in operator interface nor via a series interface, but, rather, directly from a control switch, this signal must be passed to a 7SJ62 binary input, and configured accordingly so that the ele-ment selected for high speed tripping will be effective.

Internal control function

The manual closing information must be routed via CFC (interlocking task-level) using the CMD_Information block, if the internal control function is used (see Figure 6-15).

Figure 6-15 Example for manual close feature using the internal control function

“IN: Control Device 52 Breaker CF_D12”

“OUT: P. System Data 2

>Manual Close SP”

When reclosing occurs, it is desirable to have high speed protection against temporary faults. With address  set to ZLWKDFWLYH, the 50-2 elements may be set for high speed tripping. If the fault still exists after the first reclose, the 50-2 elements can be blocked and the 50-1 and/or 51 elements will provide time delay tripping. For those situations where reclosing is disabled, the 50-2 elements are defeated and the 50-1 and/or 51 elements provide time delay tripping. In summary, setting address  to ZLWKDFWLYH defeats one-shot, high-speed tripping via the 50-2 element for those situations where automatic reclosing is disabled.

When an external automatic reclosing device is utilized, a signal indicating that the de-vice is enabled must be transmitted to the 7SJ62 relay via a binary input.

User Specified Characteristic Curves

When using DIGSI^®4 to modify settings, a dialog box is available to enter up to twenty pairs of values for a characteristic curve (see Figure 6-16).

Figure 6-16 Entry of a User Specified Characteristic Curve in DIGSI^®4

In order to represent the curve graphically, the user should click on &KDUDFWHULV

WLF. The pre-entered curve will appear as shown in Figure 6-17.

The characteristic curve shown in the graph can be modified by placing the mouse cur-sor over a point on the curve, holding down the left mouse button, and dragging the data point to the desired new position. Releasing the mouse button will automatically update the value in the value table.

The upper limits of the value ranges are shown by dotted lines at the top and right ex-tremes of the coordinate system. If the position of a data point lies outside these limits, the associated value will be set to “infinity”.

Figure 6-17 Visualization of a User Specified Characteristic Curve in DIGSI^®4

If address  was set to 8VHU'HILQHG3LFNXS&XUYH or 8VHU'HILQHG

3LFNXSDQG5HVHW&XUYH during configuration of the user-specified curve option, a maximum of 20 value pairs (current and time) may be entered at address 

1 to represent the time-current characteristic curve associated with the 51 element.

This option allows point-by-point entry of any desired curve.

If address  was set to 8VHU'HILQHG3LFNXSDQG5HVHW&XUYH during configuration of the user-specified curve option, additional value pairs (current and re-set time) may be entered at address  0RI385HV77S to represent the rere-set curve associated with the 51 element.

Current and time values are entered as multiples of the address  and  set-tings. Therefore, it is recommended that addresses  and  be initially set to

 to simplify the calculation of these ratios. Once the curve is entered, the settings at addresses  and  may be modified if necessary.

Upon delivery of the device, all time values are set at ∞, preventing pickup of the de-vice from initiating a trip signal.

When entering a user-specified curve, the following must be observed:

− Enter the data points in ascending order. The time overcurrent functions will sort the data points by current values in ascending order. The graphical representation dis-plays the data points in the order they are entered.

− As few as 10 pairs of numbers may be entered at the user’s option. Each unused pair must then be marked as unused by entering “∞” as for the time and current val-ues. It is important to view the curve to ensure that it is clear and constant.

− Current flows which are less than the smallest current value entered will not lead to an extension of the tripping time beyond the time associated with the smallest cur-rent value entered. The characteristic curve (see Figure 6-18) represents constant

The time and current value pairs are entered at address  to recreate the drop-down curve. The following must be observed:

Figure 6-18 Use of a User-Specified Curve

− Current flows which are greater than the largest current value entered will not lead to an extension of the reset time beyond the time associated with the largest current value entered. The reset curve (see Figure 6-18) represents constant reset time for currents larger than the largest current value entered.

− Current flows which are less than the smallest current value entered will not lead to a reduction of the reset time below the time associated with the smallest current val-ue entered. The reset curve (see Figure 6-18) represents constant reset time for currents smaller than the smallest current value entered.

− Current flows less than 0.05 * 51 pickup setting will cause immediate reset.