Undervoltage Load Shedding

Area undervoltage can occur when there is a lack of reactive support for the

load. This lack of reactive support manifests itself as an undervoltage condition,

with the undervoltage most severe at the load area requiring the reactive support.

As load in the transmission systems are approximately symmetrical on all three

phases, the undervoltage condition is seen on all three phases. If the power

system voltage profile over the system is viewed as a plane, the undervoltage

event from lack of reactive support can be conceptualized as a depression from

the 1.0 pu level nominal) to some lower level, with the lowest point the area of

highest reactive support requirement.

A method of gaining selectivity for load shedding is to employ multiple time

undervoltage elements. In that manner, the localized areas with the lowest voltage

(highest reactive power support requirements) are shed first.

When implementing an undervoltage load shedding scheme, it must be secure

from asymmetrical voltage depressions occurring from unbalanced faults; single

phase-to-ground, phase-to-phase, and phase-phase

to phase-ground faults as well as three-phase faults and complete system

de-energizations.

Additional Standard Features

• Sequential or Simultaneous Transfer Mode

• Bus Phase Undervoltage (27B)

• Frequency (81) and Rate of Change of Frequency (81R) for load

shedding

• Breaker Failure Source 1 and Source 2

• Bus VT Fuse‑Loss Detection (60FL)

• Auto Trip

• Auto Close

• Four dry output contacts (two trip and two close) for Source 1 and

Source 2. one lockout/ blocking output contact, and 3 programmable

output contacts (2 Form “a” and one Form “c”)

• Two Breaker Status 52b (or 52a) inputs for the Source 1 and Source

2 breakers, four programmable digital inputs

• All functions can be enabled or disabled

• Remote/Local control selection

• Device ON/OFF Control Selection

• M‑3931 Human‑Machine Interface (HMI) Module

• M‑3976 Status Module

• IRIG‑B time synchronization

• Oscillographic recording

• Two RS‑232 ports (front and rear) and one RS‑485 port* (rear)

*When using M‑3871 ISScom V10.02.XX to communicate with M‑4172

units with Firmware version V03.00.XX and higher, the RS‑485 port

(COM 3) is not available.

• S‑4200 or M‑3871 ISScom® Communications and Oscillographic

Analysis Software

Optional Features

• 5 A or 1 A models available

• 60 Hz or 50 Hz models available

• Available in vertical panel mount

• Redundant Power Supply

• External TCM and CCM available

• Ethernet port RJ‑45 10/100 Base‑T (MODBUS over TCP/IP)

• Ethernet port RJ‑45 10/100 Base‑T (IEC 61850 Protocol)

Standard Features

• 5 programmable outputs, 2 programmable inputs, and 1 self-test output

• Oscillographic recording (COMTRADE file format)

• Time-stamped sequence of events (SOE) recording for 32 events

• Metering of Voltage and Frequency

• One RS-232 port (COM1) on front and one RS-232 or 485 port (COM2) on

rear

• M-3812 IPScom® For Windows® Communications Software

• MODBUS protocol

• Supports both 50 and 60 Hz applications

• Relay voltage inputs can be directly connected (no VT required) for

voltages ≤ 480 Vac

• Continuous Self-Diagnostics

Optional Features

• M-3801D IPSplot® PLUS Oscillograph Analysis Software

• Horizontal and Vertical panel mount versions available

Standard Features

Automatic Transfer: The digital Motor Bus Transfer System (MBTS)

provides the following Automatic Transfer logic and features:

• Transfer initiated by protective relay external to the MBTS

• Automatic Transfer after a loss of the motor bus supply voltage

based on the programmable undervoltage element. This provides a

selectable backup feature if a protective relay transfer is not initiated.

• Fast Transfer with adjustable phase angle limit, delta voltage limit

and delta frequency limit

• In-Phase Transfer at the first phase coincidence if Fast Transfer is

not possible.

• Residual Voltage Transfer at an adjustable low residual voltage limit

if Fast Transfer is not possible

• Fixed Time Transfer after an adjustable time delay

• Programmable load shedding prior to initiating In‑Phase Residual

Voltage Transfer and Fixed Time Transfer

• Verify the new source (the source to which the bus is being

transferred) is healthy and within acceptable upper and lower voltage

limits

• Provides Automatic and Manual transfers of motor bus systems on Low

Voltage Switchgears in power plants and industrial processing plants to

ensure process continuity

• Automatically selects Fast, In-Phase, Residual Voltage, and Fixed

Time motor bus transfers, based on varying system conditions

• Applicable for one way and bi-directional Manual transfers

• Can be expanded to accommodate multiple breaker configurations

• Integrated control, supervisory functions, sequence of events, and

oscillograph recording in one device

• Extensive commissioning tools, including ringdown analysis

Control features:

• Control of two circuit breakers with two individual programmable

breaker closing times

• Three-breaker configuration can be provided by two M‑4172 devices

• Breaker status supervision

• Breaker failure monitoring

This M-3401 offers three-phase line to line or line to ground configuration,

optimal pickup/ seal-in time delays from 2 to 8160 cycles, and negative

sequence voltage (47S) as well as undervoltage (27S) supervisory functions

that ensure security and reliable operation.

To ensure that all data is collected during a load-shedding event the M-3401

has oscillographic recording, storing 180 cycles of all measured parameters.

Additionally, the M-3401 has a Sequence of Events (SOE) recorder built-in to

capture and store a total of 32 events with 1mSec resolution time stamp.

• Asymmetrical voltage depressions occurring from single to phase-to-ground, phase

-to-phase, and phase-phase to ground faults are detected by using a negative

sequence overvoltage element (47S) as a supervision. Typically set to 0.05 to 0.1 pu

of nominal voltage, if the adjustable threshold is exceeded, the undervoltage load

shedding is blocked.

• Three-phase faults that decrease the voltage symmetrically across all three phases,

as well as complete de-energizations of the parts of the power system due to fault

clearing or other sectionalizing, are detected by using undervoltage supervision

(27S) on all phases. The undervoltage supervision is typically set lower than the lowest

survivable undervoltage that could occur from lack of reactive support before the entire

system voltage collapses, typically from 0.9 to 0.7 pu. If any phase voltage is lower

than the adjustable setting, it is assumed that the condition is from a fault (any type,

including three-phase) or complete de-energization of that part of the system.

Description

The M-3401 Load Shedding Relay provides voltage load shedding,

frequency load shedding or supervised voltage or frequency load

shedding to assist in voltage collapse mitigation. 

The M-3401 Load Shedding Relay can be integrated into load shedding

schemes that are part of an Energy Management System (EMS), or into

automatic load shedding schemes as defined by the IEEE Power System

Relaying Committee, Substation Protection Subcommittee, Working

Group K-12.

In load shedding as part of EMS application, a control signal is sent to

multiple remote switches at participating blocks of customers to interrupt

loads for predetermined intervals. This method of load shedding can be

manually performed by dispatchers at the EMS control station, or they

may be automatic from the EMS using the logic, measurement and

intelligence of the M-3401.

In the Automatic Load Shedding scheme where voltage instability is

caused by sudden loss of critical transmission equipment or VAr

generating equipment (i.e. very short collapse time), the M-3401 provides

the means to quickly arrest fast voltage drop by disconnecting selected

large blocks of customer load allowing voltage to recover.

• Voltage Collapse Mitigation providing 4-step undervoltage and 4-step

underfrequency load shedding functions

• Undervoltage blocking and negative sequence overvoltage blocking for

system faults provides load shedding security

• Local and remote serial communications (MODBUS Protocol) for

monitoring and control functions

• 5 programmable outputs and 2 programmable inputs Protective Functions

• 4-Step Phase undervoltage (27) protection, single-phase and positive sequence

• 4-Step Phase undervoltage, selectable as single phase or positive sequence

responding, with Negative sequence overvoltage and three phase undervoltage

supervision

• Phase overvoltage (59) protection

• Four-step over/under frequency (81) protection

• Rate of Change of Frequency (81R) protection

• IPSlogic™ takes the contact INPUT status and function status and generates

OUTPUTS by employing (OR, AND, and NOT) boolean Logic and a timer.

Description

M‑3410A Intertie/Generator Protection Relay – Specification

The M-3410A Intertie/Generator Protection Relay is intended for the

protection of the intertie between the utility and dispersed generation.

It is also suitable for the protection of synchronous and induction

generators.

Communications and control features of the M-3410A are accomplished

utilizing the M-3810A IPScom for Windows Communications Software.

Oscillographic Recorder

The oscillographic recorder provides comprehensive data recording of all

monitored waveforms, input contacts, and output contacts, storing up to

120 cycles of data. The total record length is configured for one or two

partitions. A programmable post trigger delay (5 to 95%) is incorporated

to capture breaker operation.

The oscillograph is triggered remotely using the serial interface, designated

status input signals, or M-3410A programmable output operations.

Storage of oscillographic records is nonvolatile and will be retained even

without power, as long as the on-board battery is healthy.

Oscillographic data can be downloaded using serial communication in

Common Format For Transient Data Exchange (COMTRADE) format as

specified by IEEE Standard C37.111-1999.

Standard Features

• 2 programmable outputs, 2 programmable inputs, and 1 self-test output

• Oscillographic recording (COMTRADE file format)

• Time-stamped sequence of events recording for 32 events

• Metering of Voltage, Current, real and reactive Power, Power Factor,

Frequency, and Positive Sequence Impedance

• One RS-232 port (COM1) on front and one RS-232 or 485 port (COM2)

on rear

• M-3810A IPScom for Windows Communications Software

• MODBUS protocol

• Supports both 50 and 60 Hz applications

• Accepts 1 A or 5 A rated CT inputs

• Relay voltage inputs can be directly connected (no VT required) for

voltages ≤ 480 Vac

• Continuous Self-Diagnostics

M‑3410A Intertie/Generator Protection Relay – Specification

The M-3410A Intertie/Generator Protection Relay is intended for the

protection of the intertie between the utility and dispersed generation.

It is also suitable for the protection of synchronous and induction

generators.

Communications and control features of the M-3410A are accomplished

utilizing the M-3810A IPScom for Windows Communications Software.