PROTECTION AND INTERLOCKING SCHEME OF MV SWITCHGEAR

MURTAZA HUSSAIN DY, MGR, SWITCHGEAR ENGINEERING DIV.

SWITCHGEAR IEC/IS
BHEL Manufacture Switchgear as per IEC:62271-1002001, IS:3427:1997/IEC:298:1990, IS:13118:1991/ IEC:56:1987
IEC:62271-100-2001 High voltage alternating current circuit breaker.

IS:3427:1997/IEC:298:1990 AC Metal enclosed switchgear and Controlgear for rated voltage above 1 kV & upto & including 52 kV. IS:13118:1991/IEC:56:1987 Specification for High Voltage Alternating current circuit breaker.

SWITCHGEAR
A GENERAL TERM COVERING SWITCHING DEVICES AND THEIR COMBONATION WITH ASSOCIATED CONTROL, MEASUREING, PROTECTIVE AND REGULATING EQUIPMENT, ALSO ASSEMBLIES OF SUCH DEVICES AND EQUIPMENT WITH ASSOCIATED INTERCONNECTIONS, ACCESSORIES, ENCLOSURE AND SUPPORTING STRUCTURES.

CIRCUIT BREAKER
A MECHANICAL SWITCHING DEVICE CAPABLE OF MAKING, CARRYING, AND BREAKING CURRENTS UNDER NORMAL CIRCUIT CONDITIONS AND ALSO MAKING, CARRYING FOR A SPECIFIED TIME AND BREAKING CURRENTS UNDER SPECIFIED ABNORMAL CIRCUIT CONDITIONS SUCH AS THOSE OF SHORT CIRCUIT.

CHAMBERS IN SWITCHGEAR

Breaker Chamber Busbar Chamber

HT CHAMBER

CT/PT Chamber

Instrument Chamber (Relay/meters/switches etc.)

LT CHAMBER

LOCATION OF VARIOUS MAJOR COMPONENTS IN SWITCHGEAR

Circuit Breaker Current Transformer Instruments Potential Transformer Surge Suppressor Busbar
INSERT PICTURE

SWITCHGEAR IN POWER SYSTEM CAN ACT AS :

Incomer Feeder TIE Feeder Transformer Feeder Motor Feeder Bus Coupler Plant Feeder / Outgoing feeder Bus PT Line PT

Incomer Feeder: Switchgear Panel intended for supply power to the Switchboard. TIE Feeder: Switchgear panel which connects the two same voltage level switchboard. Power can flow in either direction TIE feeder. Motor Feeder: Switchgear panel employed for feeding the motor.

Transformer Feeder: Switchgear panel employed for feeding the transformer.

Plant / Outgoing Feeder: Switchgear panel employed for supply power to other switchboard. Bus PT: Switchgear panel having voltage transformer and used for the detection of bus voltage. Feeder/Line PT: Switchgear panel having voltage transformer and used for the detection of feeder/line side voltage.

TIE TIE

INCOMER INCOMER LINE PT LINE PT OUTGOING/ OUTGOING/ PLANT FDR PLANT FDR MOTOR FDR MOTOR FDR

BUS PT BUS PT

Typical Power Plant Single Line Diagram (SLD) (PART)

TRAFO FDR TRAFO FDR

SWITCHGEAR INTERLOCK SCHEME

The major functions of switchgears are protection, control and facilitating the maintenance of the electrical network including the switchgear itself. Control and inter-locking schemes constitute a very important aspect of medium voltage switchgears. The switching operation involves a variety of control and inter-locking schemes. Following are the variety of schemes which are being used:
Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

SAFETY INTERLOCKS: i) The VCB truck cannot be racked in or out unless circuit breaker is in 'Open' condition. The VCB truck can not be racked in unless secondary Plug & socket are engaged. The circuit breaker electrical closing operation is not possible unless secondary plug & socket are engaged. The secondary plug and socket can not be disengaged When the VCB truck is in 'Service or any Intermediate position between test and service positions. The circuit breaker closing operation is not possible unless the truck is in 'Service' or 'Test' position. The interlock mechanism cannot be operated unless the circuit breaker is in 'Open' condition.

ii)

iii)

iv)

v)

vi)

VII)

Inter changeability of trucks of different current ratings are not possible.

VIII)

Provision for Earthing

Earthing feature & Interlock (operation of Earthing module) a) FEB Feeder Earthing Breaker b) BEB Bus Bar Earthing Breaker

IX)

Earthing Truck (Test to Service) Limit Switch

Enable tripping of upstream/ downstream breaker Block closing of upstream/ downstream breaker

X)

Fool proof Mechanical interlock arrangement for Busbar earthing

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

CLOSING CIRCUIT : The closing circuit consists of fuses, control switch, anti pumping device, spring charged limit switch & closing coil. Closing command is executed by control switch through breaker NC contact when spring is charged. All auxiliary switch contacts position changes i.e. NO contact closes and NC contact opens. The CB can be closed manually by green coloured manual close knob provided in the mechanism box.

ANTI PUMPING : Anti pumping device prevent the CB from getting repeated closing and tripping impulses when a continuous closing command is given before the tripping impulse is withdrawn.

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

Tripping Schemes

Shunt Tripping Schemes

Series Tripping Schemes

SHUNT TRIPPING CIRCUIT :

The tripping circuit consists of fuses, control switch, protective relay & tripping coil. Breaker can be opened intentionally by control switch & on fault, breaker gets tripping command from relay. All aux. switches will restore their original positions i.e. NO will open and NC will close.

Note : The tripping spring gets charged while the closing spring is discharged.

Series Tripping Schemes

Using Relays Using Summation CT Using Motor Protection Circuit Breaker (MPCB) Using Time Limit Fuses

PANEL ILLUMINATION : 40W filament lamp is provided inside the instrument panel. The door operated panel illumination lamp gets automatically lighted on opening the door.

3 PIN SOCKET& SWITCH: 5/15 Amps, 240 V, 5 Pin socket with piano switch is also provided on the panel for hand lamp.

ANTI CONDENSATION :

Two tubular heaters with thermostat and piano switch are provided for anti condensation in breaker chamber and CT chamber.

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

Trip Circuit Supervision Schemes

The Trip circuit extends beyond the protection relay and other components such as fuses, relay contacts, switches etc requires considerable amount of circuit breaker wiring with intermediate terminal boards. These interconnections coupled with the importance of the circuit, results in the requirement to monitor the integrity of the circuit .

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

Voltage Selection Schemes

Need for Voltage Selection scheme ?

Voltage signals to instruments and meters mounted on switchgear panels are derived from the potential transformer (PTs). These PTs are either Bus connected or Feeder connected. Incase of fault any source feeder, arrangement should be made in such a way that PT signal should be available to meters and instruments

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

Alarm Schemes

Alarm Cancellation Scheme Alarm Annunciation Scheme

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

Synchronizing Schemes
To bring new bus (source) into the switchboard when old one is running and shifting to new one. To meet synchronizism that means two AC supplies are correctly paralleled following condition should be satisfied. a) The voltages of the two supplies must be within acceptable limits. b) The frequencies of the two supplies must be within acceptable limits. c) The phase difference of the two supplies must be within acceptable limits. Methods adopted for synchronization are : Manual Synchronization By Check Synchronizing Relays A check synchronizing relay is used to prevent inter-connection of two badly synchronized supplied. Its dual purpose is to Safeguard manual synchronizing.

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

SWITCHGEAR INTERLOCK SCHEME

Safety Interlocks & schemes using position limit switches; Closing Scheme; Tripping schemes; Trip circuit supervision schemes; Voltage selection schemes; Alarm schemes, Synchronizing schemes and Automatic supply transfer schemes.

Automatic Supply Transfer Schemes

Requirement of Automatic Bus Transfer Scheme ? Unit Switchgear Station Switchgear

Modes of Bus Transfer

A. Manual Bus Transfer i) Without Voltage Interruption ii) With Voltage Interruption a) Slow changeover b) Fast changeover B. Automatic Bus Transfer (under fault condition) with Voltage Interruption a) Slow changeover b) Fast changeover

Electrical Interlock Electrical Interlock in Closing Circuit in Closing Circuit

Electrical Interlock Electrical Interlock in Tripping Circuit in Tripping Circuit

Electrical Interlocking scheme is guided by the logic diagram.

Protection Schemes for Medium Voltage Switchgear

Importance of Protection System in Electrical System ? 5-S Security Principles : Protective system should be reliable so that security of supply is ensured.

Sensitivity : Protective system should be able to sense minimum value of fault current, thereby reducing the consequent damage. Speed : Protective system should be able to isolate fault in the shortest possible time. Selectivity : Protective system should be able to select and trip only the nearest circuit breaker. Stability : Protective system should not operate for external faults.

FAULT : It is defined as any abnormal condition, which causes reduction in the basic insulation level strength of system. FAULT DETECTION : POSITIVE, NEGATIVE & ZERO Phase sequence component of system.

PROTECTION SCHEMES IN MV SWITCHGEAR

Non Directional Over Current for Phase Faults (50/51) Non Directional Over Current for Earth Fault (50N/51N) Directional Over Current for Phase Faults (67) Directional Over Current for Earth Fault (67N)

UNIT PROTECTION SCHEME

In Unit Protection sections of power system are protected individually as a complete unit without reference to other section. Some of the Unit scheme which MV Switchgear employed Pilot Wire Protection Scheme For the protection of CABLE connecting two Feeder Bus Differential Protection Scheme For the protection of BUSBAR Motor/ Transformer Differential Protection Scheme For the protection of MOTOR/ TRANSFORMER WINDINGS Restricted Earth Protection Scheme For the protection of TRANSFORMER WINDINGS

TRANSFORMER PROTECTION

Non- Directional Over Current and Earth Fault Protection (50/51/50N/51N) Sensitive Earth Fault Protection (50N/2) Differential Protection (87T) Restricted Earth Fault Protection (64R) Incipient Faults (49/63TX)

MOTOR PROTECTION

Wide range of A.C Motors Motor characteristics due to various duties All Motor needs protection and choice should be independent of a type of motor & load connected.

NEED FOR PROTECTION

Allowing operation under normal conditions. Quick isolation from supply under abnormal conditions. Averting damage to the motor & driven mechanism. Enhancement of life of motor.

A. MOTOR INDUCED

MOTOR PROTECTION
1. INSULATION FAILURE 2. BEARING FAILURE 3. MECHANICAL FAILURE 4. LOSS OF FIELD (SYNCHRONOUS MOTOR)

B. LOAD INDUCED

1. OVERLOAD/ UNDERLOAD 2. JAMMING 3. HIGH INERTIA 1. HIGH AMBIENT TEMPERATURE 2. HIGH CONTAMINATED LEVEL-BLOCKED VENTILATION 3. COLD, DAMP AMBIENT TEMPERATURE

C. ENVIRONMENT INDUCED

D. SOURCE OR SYSTEM INDUCED

1. PHASE FAILURE 2. OVER VOLTAGE/UNDER VOLTAGE 3. PHASE REVERSAL 4. OUT-OF-STEP

E. OPERATION AND APPLICATION INDUCED

1. SYNCHRONIZING, CLOSING OR RECLOSING OUT OF PHASE 2. HIGH DUTY CYCLE 3. JOGGING

MOTOR PROTECTION
Thermal Over Load protection (49) Single phasing/ Negative Phase Sequence Protection (46) Short-circuits between phases or between phase and earth in the motor winding or its connections. (50/51) Partial or complete collapse of voltage (27) Locked rotor (51S) Start or Stall Protection(48/51LR) Earth Fault Protection (50N) Loss-Of-Load Protection (37) Out of Step Protection (46) RTD/BTD Protection (26) Limitation of the number of start, Time between start (66)

PROTECTION AGAINST SWITCHING SURGES: What is an Electrical Surge ? External surge & Internal surge

Atmospheric Lightning cause External surge Switching action of devices cause internal surge

CAUSES OF SURGE GENERATION: Normal Switching On of a stationary motor. Normal switching Off of a stationary motor. Switching a Stalled motor or one running upto speed.

PROTECTION AGAINST SWITCHING SURGES:

SURGE

PROTECTION DEVICES:

These devices limits the over voltages in electrical system to the specified protection level, principally lower than the withstand voltage of equipment.

a/ C-R type surge suppressors. b/ ZnO type surge arrestors.

CUSTOMER SPECIFIC SCHEME

BUS DIFFERENTIAL

PILOT WIRE PROTECTION

MOTOR RE-ACCELERATION

MOTOR DIFFERENTIAL

TWO OUT OF THREE BREAKER SCHEME

REVERSE BLOCKING SCHEME MECHANICAL INTERLOCKING SCHEME

NUMERICAL RELAYS AND COMMUNCATION SYSTEM

SYSTEM ON UCA2- IEC 61850

OPERATOR INTERFACE HMI & MAINTENANCE WEB access NR

NR

NR

FAST ETHERNET UCA2- IEC 61850

HV FEEDER BAYS

DC DC NR NR Main protection EHV FEEDER BAY I/Os I/Os NR COMMON BAY NR MV FEEDER BAYS NR NR NR

NR

NR

NR

FIG: 1

MV FEEDER BAYS

To ECS

HMI

Redundant Modbus RTU Link (RS 485)

GATEWAY

Laserjet Printer Ethernet Switch Ethernet Switch

Numerical Relays

Numerical Relays NR NR NR NR GPS

NR

NR

08 07 06 05 04 03

02
CPU

01

08 07 06 05 04 03

02
CPU

01

BIU 24x

Data Concentrator

Data Concentrator

NR
Ethernet Modbus (RS 485) Co-Axial Cable

NR

NR

NR

NR

BIU 24x

NR

NR

NR

Numerical Relays

Numerical Relays

FIG : 2

HMI
PROGRAMMER ROOM

LASER PRINTER

HMI

TO STATION LAN

FO
CER ROOM

FO DATA CONCENTRATOR DATA CONCENTRATOR

FO
TO DDCMIS (ON OPC)

TO DDCMIS (ON OPC)

MV SWGRS
SWITCH SWITCH SWITCH SWITCH SWITCH SWITCH

ETHERNET SWITCHES (IEC61850) 16/8 CHANNEL NUMERICALRELAYS IN SWGR PANELS

LT SWGRS
SWITCH SWITCH SWITCH SWITCH SWITCH SWITCH

FIG : 4

LOCATION CENTRAL CONTROL ROOM

TO MAIN SCADA

DATA CONCENTRATOR FO FO

(TYPICAL)

DATA CONCENTRATOR

TO MAIN SCADA

33KV SWGRS

SWITCH

SWITCH

(TYPICAL)

ETHERNET SWITCHES (IEC61850) 16/8 CHANNEL

11KV
SWITCH SWITCH

SWGRS

(TYPICAL)

NUMERICALRELAYS IN SWGR PANELS

LT
SWITCH

(TYPICAL)

SWITCH

SWITCH

SWGRS

FIG : 5

STAR ARCHITECTURE
SCADA/EMS

GATEWAY substation level

OI

ETHERNET SWITCH

DC NR

DC NR

DC NR

NR

NR

NR

NR

NR

NR

FIG : 6

REDUNDANT RING ARCHITECTURE

SCADA/EMS

GATEWAY substation level ETHERNET SWITCH

OI

DC DC DC NR NR

C264
NR

NR

FIG : 7

DOUBLE REDUNDANT RING ARCHITECTURE

SCADA/EMS OI GATEWAY

ETHERNET SWITCH

ETHERNET SWITCH

LAN n1

LAN n2

LAN: Local Area Network

DC DC

NR

FIG : 8
NR

NR

NR

Communication Standards Overview

Indications Commands Measured and MeteredValues Time Synchronisation Fault Records International StandardInteroperability Process Bus Communication Engineering support Data Transmission Transmission Speed [Mbit/s]

IEC 103

PROFIBUS DNP V3.00

Modbus without time stamp

UCA2

IEC 61850

No No Master/ Slave 0.19

No

No

Event Driven 100

without without time stamp time stamp

No No

No No No

No No Master/ Slave 12

No No Master/ Slave 0.12

No No Master/ Slave 0.12

No No Event driven 100

CABLE DIFFERENTIAL PROTECTION

CABLE DIFFERENTIAL PROTECTION

REVERSE BLOCKING LOGIC

Reverse blocking principle is adopted to cut down the grading time of upstream breaker of HT stream. The down stream protection when operated on a fault shall block upstream protection. For this one contact of short circuit and earth fault protection of each outgoing feeder on one switchboard shall be paralleled, and connected to digital input of numerical relay in incomer panel. The digital input if not energized allows the fast operation of upstream protection. however, delay protection shall always be available

INCOMER LOGIC

TIE FEEDER LOGIC

MECHANICAL INTERLOCKING SCHEME

WHY SUCH SCHEME IS REQUIRED ? It is required to prevent opening of CT cum CABLE termination & Busbar chamber under live-circuit condition. BASIC PRINCIPLE OF OPERATION :Under this scheme rear side bolted covers can be removed only when specific key is applied on CASTELL type mechanical interlocks located on covers and key is rotated 90 deg. Clockwise.

The mechanical interlocks and keys are arranged to achieve following requirements :

For opening of the Bolted covers of CT/Cable Chamber of Outgoing feeder For opening the bolted covers of CT/Cable chamber of Incomer feeders panels For opening the bolted covers of the bus chamber of any panel

THANK YOU