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Siemens 7SR21 Manual

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7SR21 Non-Directional
7SR22 Directional
Overcurrent Relay

Document Release History

This document is issue 2010/05. The list of revisions up to and including this issue is:
2010/05
Typographical revisions
2010/02
Document reformat due to rebrand
2009/09
Third Issue. Software revision 2435H80004/5 R4b-4
2008/07
Second issue. Software revision 2435H80004/5 R3d-3.
2008/03
First issue

Software Revision History

2009/09
2435H80004/5 R4b-4
2008/07
2435H80004/5R3d-3
2008/03
2435H80004/5R2c-2b
The copyright and other intellectual property rights in this document, and in any model or article produced from it
(and including any registered or unregistered design rights) are the property of Siemens Protection Devices
Limited. No part of this document shall be reproduced or modified or stored in another form, in any data retrieval
system, without the permission of Siemens Protection Devices Limited, nor shall any model or article be
reproduced from this document unless Siemens Protection Devices Limited consent.
While the information and guidance given in this document is believed to be correct, no liability shall be accepted
for any loss or damage caused by any error or omission, whether such error or omission is the result of
negligence or any other cause. Any and all such liability is disclaimed.
©2010 Siemens Protection Devices Limited
CTS-I Supervision. Undercurrent 37G & 37SEF. Vx U/O Voltage. 46BC
U/C. Comms Settings. Waveform Storage Settings. Fault Storage
Settings. Energy Storage. Trip test function. Local/Remote modes.
Settings ranges extended. Protocol changes.
Demand records. Optional DNP3.0 data comms.
First Release
7SR21 & 7SR22 Argus Applications Guide
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  • Page 1: Document Release History

    Limited. No part of this document shall be reproduced or modified or stored in another form, in any data retrieval system, without the permission of Siemens Protection Devices Limited, nor shall any model or article be reproduced from this document unless Siemens Protection Devices Limited consent.

  • Page 2: Table Of Contents

    7SR21 & 7SR22 Argus Applications Guide Contents Document Release History........................1 Software Revision History........................1 Contents ..............................2 Section 1: Common Functions ......................4 1.1 Multiple Settings Groups......................4 1.2 Binary Inputs ..........................5 1.3 Binary Outputs ..........................8 1.4 LEDs ............................8 Section 2: Protection Functions ......................10 2.1 Time delayed overcurrent (51/51G/51N) ................10...
  • Page 3 7SR21 & 7SR22 Argus Applications Guide 5.2 Current Transformer Supervision (60CTS)................35 5.3 Voltage Transformer Supervision (60VTS)................36 5.4 Trip-Circuit Supervision (74TCS) ....................37 5.4.1 Trip Circuit Supervision Connections .................37 5.5 Inrush Detector (81HBL2) .......................39 5.6 Broken Conductor / Load Imbalance (46BC)................39 5.7 Circuit-Breaker Maintenance ....................39 List of Figures Figure 1.1-1 Example Use of Alternative Settings Groups ..............4...

  • Page 4: Section 1: Common Functions

    7SR21 & 7SR22 Argus Applications Guide Section 1: Common Functions Multiple Settings Groups Alternate settings groups can be used to reconfigure the relay during significant changes to system conditions e.g. Primary plant switching in/out. Summer/winter or day/night settings. switchable earthing connections.

  • Page 5: Binary Inputs

    7SR21 & 7SR22 Argus Applications Guide Binary Inputs Each Binary Input (BI) can be programmed to operate one or more of the relay functions, LEDs or output relays. These could be used to bring such digital signals as Inhibits for protection elements, the trip circuit supervision status, autoreclose control signals etc.
  • Page 6 7SR21 & 7SR22 Argus Applications Guide The Effects of Capacitance Current The binary inputs have a low minimum operate current and may be set for instantaneous operation. Consideration should be given to the likelihood of mal-operation due to capacitance current. Capacitance current can flow through the BI for example if an earth fault occurs on the dc circuits associated with the relay.

  • Page 7: Figure 1.2-2 - Binary Input Configurations Providing Compliance With Eats 48-4 Classes

    7SR21 & 7SR22 Argus Applications Guide Figure 1.2-2 – Binary Input Configurations Providing Compliance with EATS 48-4 Classes ESI 1 and ESI 2 ©2010 Siemens Protection Devices Limited Chapter 7 Page 7 of 39...

  • Page 8: Binary Outputs

    7SR21 & 7SR22 Argus Applications Guide Binary Outputs Binary Outputs are mapped to output functions by means of settings. These could be used to bring out such digital signals as trips, a general pick-up, plant control signals etc. All Binary Outputs are Trip rated Each can be defined as Self or Hand Reset.

  • Page 9: Figure 1.4-2 Led Configuration Via The Settings \ Output Config \ Led Config Menu

    7SR21 & 7SR22 Argus Applications Guide In the OUTPUT CONFIG\LED CONFIG menu in the Settings tab, to assign the required LED as a particular colour, either red or green, type the LED number in the appropriate row. To assign the required LED as a yellow colour, type the LED number in both red and green rows.

  • Page 10: Section 2: Protection Functions

    7SR21 & 7SR22 Argus Applications Guide Section 2: Protection Functions Time delayed overcurrent (51/51G/51N) The 51-n characteristic element provides a number of time/current operate characteristics. The element can be defined as either an Inverse Definite Minimum Time Lag (IDMTL) or Definite Time Lag (DTL) characteristic. If an IDMTL characteristic is required, then IEC, ANSI/IEEE and a number of manufacturer specific curves are supported.

  • Page 11: Selection Of Overcurrent Characteristics

    7SR21 & 7SR22 Argus Applications Guide 1000.00 100.00 10.00 1.00 0.10 0.01 1000 Current (x Is) Figure 2.1-2 IEC NI Curve with Minimum Operate Time Setting Applied To increase sensitivity, dedicated Earth fault elements are used. There should be little or no current flowing to earth in a healthy system so such relays can be given far lower pick-up levels than relays which detect excess current ( >...

  • Page 12: Reset Delay

    7SR21 & 7SR22 Argus Applications Guide OC/EF Curve Characteristic Application IEC Normal Inverse (NI) Generally applied ANSI Moderately Inverse (MI) IEC Very Inverse (VI) Used with high impedance paths where there is a significant difference between fault levels at protection points...

  • Page 13: Voltage Dependent Overcurrent (51V)

    7SR21 & 7SR22 Argus Applications Guide Voltage dependent overcurrent (51V) Reduced voltage can indicate a fault on the system, it can be used to make the 51 elements more sensitive. Typically Voltage Dependent Over-current (51V) is applied to: Transformer Incomers: Where the impedance of the transformer limits fault current the measured voltage level can be used to discriminate between load and fault current.

  • Page 14: Instantaneous Overcurrent (50/50G/50N)

    7SR21 & 7SR22 Argus Applications Guide Instantaneous Overcurrent (50/50G/50N) Each instantaneous element has an independent setting for pick-up current and a follower definite time lag (DTL) which can be used to provide time grading margins, sequence co-ordination grading or scheme logic. The “instantaneous”...

  • Page 15: Figure 2.4-2 Blocking Scheme Using Instantaneous Overcurrent Elements

    7SR21 & 7SR22 Argus Applications Guide Figure 2.4-2 Blocking Scheme Using Instantaneous Overcurrent Elements Typically a time delay as low as 50ms on the incomer 50-1 element will ensure that the incomer is not tripped for outgoing circuit faults. However, to include for both equipment tolerances and a safety margin a minimum time delay of 100ms is recommended.

  • Page 16: Sensitive Earth-Fault Protection (50Sef)

    7SR21 & 7SR22 Argus Applications Guide Sensitive Earth-fault Protection (50SEF) Earth fault protection is based on the assumption that fault current levels will be limited only by the earth fault impedance of the line and associated plant. However, it may be difficult to make an effective short circuit to earth due to the nature of the terrain e.g.

  • Page 17: Directional Protection (67)

    7SR21 & 7SR22 Argus Applications Guide Directional Protection (67) Each overcurrent stage can operate for faults in either forward or reverse direction. Convention dictates that forward direction refers to power flow away from the busbar, while reverse direction refers to power flowing towards the busbar.

  • Page 18: Figure 2.6-3 Application Of Directional Overcurrent Protection

    7SR21 & 7SR22 Argus Applications Guide Directional overcurrent elements allow greater fault selectivity than non-directional elements for interconnected systems where fault current can flow in both directions through the relaying point. Consider the network shown in fig. 2.6-3. The Circuit breakers at A, B, E and G have directional overcurrent relays fitted since fault current can flow in both directions at these points.

  • Page 19: Figure 2.6-4 Feeder Fault On Interconnected Network

    7SR21 & 7SR22 Argus Applications Guide Fault 1 Load Figure 2.6-4 Feeder Fault on Interconnected Network Considering the D-G feeder fault shown in fig. 2.6-4: the current magnitude through breakers C and D will be similar and their associated relays will similar prospective operate times. To ensure that only the faulted feeder is isolated G FWD must be set to be faster than C.

  • Page 20: Directional Earth-Fault (50/51G, 50/51N, 51/51Sef)

    7SR21 & 7SR22 Argus Applications Guide Directional Earth-Fault (50/51G, 50/51N, 51/51SEF) The directional earth-fault elements, either measure directly or derive from the three line currents the zero sequence current (operate quantity) and compare this against the derived zero phase sequence voltage (polarising quantity).

  • Page 21: High Impedance Restricted Earth Fault Protection (64H)

    The calculation of the value of the Stability Resistor is based on the worst case where one CT fully saturates and the other balancing CT does not saturate at all. A separate Siemens Protection Devices Limited Publication is available covering the calculation procedure for REF protection. To summarise this: The relay Stability (operating) Vs voltage is calculated using worst case lead burden to avoid relay operation for through-fault conditions where one of the CTs may be fully saturated.

  • Page 22: Figure 2.8-2 Composite Overcurrent And Restricted Earth-Fault Protection

    7SR21 & 7SR22 Argus Applications Guide Composite overcurrent and REF protection can be provided using a multi-element relay as. overcurrent elements series stabilising resistor element non-linear resistor Figure 2.8-2 Composite Overcurrent and Restricted Earth-fault Protection Although core-balance CTs are traditionally used with elements requiring sensitive pickup settings, cost and size usually precludes this on REF schemes.

  • Page 23: Negative Phase Sequence Overcurrent (46Nps)

    7SR21 & 7SR22 Argus Applications Guide Negative Phase Sequence Overcurrent (46NPS) The presence of Negative Phase Sequence (NPS) current indicates an unbalance in the phase currents, either due to a fault or unbalanced load. NPS current presents a major problem for 3-phase rotating plant. It produces a reaction magnetic field which rotates in the opposite direction, and at twice the frequency, to the main field created by the DC excitation system.

  • Page 24: Under/Over Voltage Protection (27/59)

    7SR21 & 7SR22 Argus Applications Guide 2.12 Under/Over Voltage Protection (27/59) Power system under-voltages on may occur due to: System faults. An increase in system loading, Non-energized power system e.g. loss of an incoming transformer During normal system operating conditions regulating equipment such as transformer On Load Tap Changers (OLTC) and generator Automatic Voltage Regulators (AVR) ensure that the system runs within acceptable voltage limits.

  • Page 25: Neutral Overvoltage (59N)

    7SR21 & 7SR22 Argus Applications Guide 2.13 Neutral Overvoltage (59N) Neutral Overvoltage Displacement (Residual Overvoltage) protection is used to detect an earth fault where little or no earth current flows. This can occur where a feeder has been tripped at its HV side for an earth fault, but the circuit is still energised from the LV side via an unearthed transformer winding.

  • Page 26: Application With Capacitor Cone Units

    7SR21 & 7SR22 Argus Applications Guide 2.13.1 Application with Capacitor Cone Units Capacitor cones provide a cost effective method of deriving residual voltage. The wide range of capacitor cone component values used by different manufacturer’s means that the relay cannot be connected directly to the cones.

  • Page 27: Under/Over Frequency (81)

    7SR21 & 7SR22 Argus Applications Guide 2.15 Under/Over Frequency (81) During normal system operation the frequency will continuously vary over a relatively small range due to the changing generation/load balance. Excessive frequency variation may occur for: Loss of generating capacity, or loss of mains supply (underfrequency): If the governors and other regulating equipment cannot respond to correct the balance, a sustained underfrequency condition may lead to a system collapse.

  • Page 28: Section 3: Ct Requirements

    7SR21 & 7SR22 Argus Applications Guide Section 3: CT Requirements CT Requirements for Overcurrent and Earth Fault Protection 3.1.1 Overcurrent Protection CTs a) For industrial systems with relatively low fault current and no onerous grading requirements - a class 10P10 with VA rating to match the load.

  • Page 29: Section 4: Control Functions

    7SR21 & 7SR22 Argus Applications Guide Section 4: Control Functions 4.1 Auto-reclose Applications Automatic circuit reclosing is extensively applied to overhead line circuits where a high percentage of faults that occur are of a transient nature. By automatically reclosing the circuit-breaker the function attempts to minimise the loss of supply to the customer and reduce the need for manual intervention.

  • Page 30: Auto-Reclose Example 1

    7SR21 & 7SR22 Argus Applications Guide The relay closest to the fault (D) would step through its Instantaneous Trips in an attempt to clear the fault. If unsuccessful, the relay would move to a Delayed Trip sequence. The other relays in the network (A, B and C) would recognise the sequence of Pick-up followed by current switch- off as ARC sequences.

  • Page 31: Auto-Reclose Example 2 (Use Of Quicklogic With Ar)

    7SR21 & 7SR22 Argus Applications Guide 4.1.2 Auto-Reclose Example 2 (Use of Quicklogic with AR) Figure 4.1-2 Example of Logic Application Requirement: The relay at location ‘A’ it is required to provide a reclose sequence of 2 Instantaneous followed by 2 delayed recloses.

  • Page 32: Quick Logic Applications

    7SR21 & 7SR22 Argus Applications Guide 4.2 Quick Logic Applications 4.2.1 Auto-Changeover Scheme Example INCOMER 1 INCOMER 2 Start On-Load Start On-Load Change-over Change-over BI 1 OPEN Busbar 1 Busbar 2 LOADS LOADS Figure 4.2-1 Example Use of Quick Logic The MV installation illustrated above is fed from two incomers.

  • Page 33: Section 5: Supervision Functions

    7SR21 & 7SR22 Argus Applications Guide Section 5: Supervision Functions Circuit-Breaker Fail (50BF) Where a circuit breaker fails to operate to clear fault current the power system will remain in a hazardous state until the fault is cleared by remote or back-up protections. To minimise any delay, CB Failure protection provides a signal to either re-trip the local CB or back-trip ‘adjacent’...

  • Page 34: Figure 5.1-2 - Single Stage Circuit Breaker Fail Timing

    7SR21 & 7SR22 Argus Applications Guide The time delays run concurrently within the relay. The time delay applied to the CB Fail protection must be in excess of the longest CB operate time + relay reset time + a safety margin.

  • Page 35: Current Transformer Supervision (60Cts)

    7SR21 & 7SR22 Argus Applications Guide Current Transformer Supervision (60CTS) When a CT fails, the current levels seen by the protection become unbalanced. A large level of NPS current is therefore detected - around 0.3 x In for one or two CT failures. However this condition would also occur for a system fault.

  • Page 36: Voltage Transformer Supervision (60Vts)

    7SR21 & 7SR22 Argus Applications Guide Voltage Transformer Supervision (60VTS) Although VTs rarely fail themselves, VT Supervision presents a common application because of the failure of protective Fuses connected in series with the VTs. When a VT failure occurs on one or two phases, the voltage levels seen by the protection become unbalanced. A large level of NPS voltage is therefore detected - around 0.3 x Vn for one or two VT failures.

  • Page 37: Trip-Circuit Supervision (74Tcs)

    7SR21 & 7SR22 Argus Applications Guide Trip-Circuit Supervision (74TCS) Binary Inputs may be used to monitor the integrity of the CB trip circuit wiring. A small current flows through the B.I. and the trip circuit. This current operates the B.I. confirming the integrity of the auxiliary supply, CB trip coil, auxiliary switch, C.B.

  • Page 38: Figure 5.4-2:Trip Circuit Supervision Scheme 2 (H6)

    7SR21 & 7SR22 Argus Applications Guide Scheme 2 (Intermediate) TRIP COIL TRIP CCT n FAIL Circuit Breaker H6 Scheme Notes: BO 1 BO n Resistor: 30V dc Nominal: R = 3K9 Remote 48V dc Nominal: R = 5K6 Alarm 110V dc Nominal: R = 15K0 Figure 5.4-2: Trip Circuit Supervision Scheme 2 (H6)

  • Page 39: Inrush Detector (81Hbl2)

    7SR21 & 7SR22 Argus Applications Guide Inrush Detector (81HBL2) This element detects the presence of high levels of 2nd Harmonic current which is indicative of transformer Inrush current at switch-on. These currents may be above the operate level of the overcurrent elements for a short duration and it is important that the relay does not issue an incorrect trip command for this transient network condition.

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