5 Management Function
6.6 Analog Input Module (NR4412)
The analog input module can transform high AC input values to relevant low AC output value, which are suited to the analog inputs of the main CPU module. The transformers are used both to step-down the currents and voltages to levels appropriate to the relay’s electronic circuitry and to provide effective isolation between the relay and the power system. A low pass filter circuit is connected to each transformer (CT or VT) secondary circuit for reducing the noise of each analog AC input signal.
NOTE! The rated value of the current transformer is optional: 1A or 5A. The rated value of the CT must be definitely declared in the technical scheme and the contract.
NOTE! Because the rated value of the current transformer is optional, it is necessary to check whether the rated value of the current transformer inputs is according to the demand of the engineering scheme before the device is put into operation.
DANGER! Never allow the current transformer (CT) secondary circuit connected to this relay to be opened while the primary system is energized. The opened CT secondary circuit will produce a dangerously high voltage. If this safety precaution is disregarded, personal death, severe personal injury or considerable equipment damage will occur.
There are two types of analog input modules: NR4412 with 26 pins and NR4412 with 24 pins. The view of the analog input module is shown in Figure 6.6-1.
01 02
Figure 6.6-1 View of the analog input module
A 26-pin or 24-pin connector is fixed on the front side of this module. The terminal definition of the connector is described as below.
Pin connections on the connector of the analog input module NR4412 with 26 pins:
Pin No. Sign Description
01 Ua 02 Ub 03 Uc 04 Un
The three voltage inputs with inner star connection (Y) for protection and metering.
05 Ux
06 Uxn The synchro-check voltage input.
07 U0
08 U0n The zero sequence voltage input.
09 I02
10 I02n The input of the No.2 zero sequence current.
11 Ia
12 Ian The input of the current of the A phase for protection.
13 Ib
14 Ibn The input of the current of the B phase for protection.
15 Ic
16 Icn The input of the current of the C phase for protection.
17 I01
18 I01n The input of the No.1 zero sequence current.
19 I0s
20 I0sn The input of the sensitive zero sequence current.
21 Iam
22 Iamn The input of the current of the A phase for metering.
23 Ibm
24 Ibmn The input of the current of the B phase for metering.
25 Icm
26 Icmn The input of the current of the C phase for metering.
Pin connections on the connector of the analog input module NR4412 with 24 pins:
Pin No. Sign Description
01 Ua 02 Ub 03 Uc 04 Un
The three voltage inputs with inner star connection (Y) for protection and metering.
05 Ux
06 Uxn The synchro-check voltage input.
07 U0
08 U0n The zero sequence voltage input.
09 I02
10 I02n The input of the No.2 zero sequence current.
11 Ia
12 Ian The input of the current of the A phase for protection.
13 Ib
14 Ibn The input of the current of the B phase for protection.
15 Ic
16 Icn The input of the current of the C phase for protection.
17 I01
18 I01n The input of the No.1 zero sequence current.
19 I0s
20 I0sn The input of the sensitive zero sequence current.
21 Not used
22 Not used
23 Not used
24 Not used
6.6.1 Connection Examples
Some connection examples of the current transformers and voltage transformers which are supported by this relay are shown in this section. If one of the analog inputs has no input in a practical engineering, the relevant input terminals should be disconnected.
1. Current connections examples
Figure 6.6-2 Current connection examples
Where:
(1) Current connections to three current transformers with a star-point connection for ground current (zero sequence current or residual current).
(2) Current connections to three current transformers with a separate ground current transformer (summation current transformer or core balance current transformer).
(3) Current connections to two current transformers with a separate ground current transformer (summation current transformer or core balance current transformer), only for ungrounded or compensated networks.
(4) Current connection to a core balance neutral current transformer for sensitive ground fault detection, only for ungrounded or compensated networks.
(5) Current connection to a separate ground current transformer (summation current transformer or core balance current transformer) for the No.2 zero sequence current input of this relay.
2. Voltage connections examples
A B C
Figure 6.6-3 Voltage connection examples
Where:
(1) Voltage connections to three star-connected voltage transformers with open-delta windings and additionally to any phase voltage (for synchronism check).
(2) Voltage connections to three star-connected voltage transformers with open-delta windings and additionally to any phase-to-phase voltage (for synchronism check).
6.6.2 Current Transformer Requirements
z CT Requirements
-- Rated primary current “Ipn”:
According to the rated current or maximum load current of primary apparatus -- Rated continuous thermal current “Icth”:
According to the maximum load current
-- Rated short-time thermal current “Ith” and rated dynamic current “Idyn”:
According to the maximum fault current -- Rated secondary current “Isn”
-- Accuracy limit factor “Kalf”:
Ipn Rated primary current (amps)
Icth Rated continuous thermal current (amps) Ith Rated short-time thermal current (amps) Idyn Rated dynamic current (amps)
Isn Rated secondary current (amps) Kalf Accuracy limit factor: Kalf = Ipal / Ipn
Ipal Rated accuracy limit primary current (amps)
z Performance Verification Esl > Esl’
Esl
Rated secondary limiting e.m.f (volts):
Esl = kalf × Isn × (Rct + Rbn)
Esl’ Required secondary limiting e.m.f (volts):
Esl’ = k × Ipcf × Isn × (Rct + Rb) / Ipn
Kalf Accuracy limit factor: Kalf = Ipal / Ipn
k Stability factor: k = 2
Ipal Rated accuracy limit primary current (amps)
Ipcf
Protective checking factor current (amps): same as the maximum prospective fault current
Ipn Rated primary current (amps) Isn Rated secondary current (amps)
Rct Current transformer secondary winding resistance (ohms) Rbn Rated resistance burden (ohms): Rbn = Sbn / Isn2
Sbn Rated burden (VAs)
Rb
Real resistance burden (ohms):
Rb = Rr + 2RL + Rc
Rc Contact resistance, 0.05~0.10 (ohms)
RL Resistance of a single lead from relay to the CT (ohms) Rr Impedance of relay phase current input (ohms)
z Example
Kalf = 30.00, Isn = 5A, Rct = 1.00Ω, Sbn = 60VA
Esl = kalf × Isn × (Rct + Rbn) = kalf × Isn × (Rct + Sbn / Isn2) So, Esl = 30 × 5 × (1 + 60 / 52) = 510V
Ipcf = 40000A, RL = 0.50Ω, Rr = 0.10Ω, Rc = 0.10Ω, Ipn = 2000A Esl’ = k × Ipcf × Isn × (Rct + Rb) / Ipn = k × Ipcf × Isn × (Rct + (Rr + 2RL + Rc)) / Ipn
So, Esl’ = 2 × 40000 × 5 × (1 + (0.1 + 2 × 0.5 + 0.1)) / 2000 = 440V It can meet the requirement: Esl > Esl’.