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Overcurrent Elements

The 889 can be used to provide backup protection for transformer

and adjacent power system equipment. Instantaneous overcurrent

(IOC) elements can be used for fast clearing of severe internal and

external (through) faults. Up to six time overcurrent protection

(TOC) elements per winding allow to coordinate with the adjacent

protection zones and act as backup protection.

• IOC protection functions are provided for phase, neutral &

ground currents

• TOC protection functions are provided for phase, neutral and

ground currents. A variety of standard time curves including

IEEE, IEC, GE Vernova IAC, I2t, definite time are provided

• FlexCurves to coordinate with adjacent protections (including

fuses) as well as transformer damage curves and thermal/

damage curves for downstream equipment Directional

protection functions are provided for phase, neutral and ground

currents. The voltage memory function enables a more reliable

relay operation, especially for faults close to the VTs.

Out of Step Protection

The out-of-step element provides out of step (loss-of-synchronism

or pole slip) tripping function for generators. The element is simplified

using a single blinder operating characteristic with an offset

mho supervisory. It is easy to apply based on IEEE/ANSI C37.102

guidelines, and IEEE PES PSRC tutorial on generator protection.

The purpose of the supervisory mho is to prevent operation on

stable swings that pass through both blinders and outside the mho

characteristic. In addition, the out-of-step tripping feature allows

“MHO EXIT” trip mode to reduce stresses on the circuit breaker.

Stator Thermal Protection

The 889 provides thermal overload protection as per IEC 60255-8

to prevent generator damage caused by generator overheating.

The 889 can be configured to trip the generator offline when the

generator’s thermal limits are reached, or close an Alarm contact

that signals operations personnel to take appropriate actions.

Sensitive Directional Power

The 889 provides low forward power and reverse power elements

to prevent generator motoring that can cause damage the

prime mover. Independent settings for power pickup levels and

operational delays are available for both alarming and tripping of

each element.

The 889 directional power element responds to three-phase

directional power and is designed for reverse power (32REV) and

low forward power (32FWD) applications for interconnections

involving co-generation.

Loss of Excitation

Supporting application flexibility, the 889 offers two methodologies

to support loss of excitation detection. This can be done through

an impedance-based approach or a Reactive Power approach.

Unlike the Impedance based function, the Reactive Power Function

settings do not need machine parameters for setting and can be

used in cases where machine parameters are not available.

100% Stator Ground Fault Protection

The 889 provides 100% Stator Ground Fault Protection for High

Resistance Grounded System (HRG), Low Resistance Grounded

(LRG) or Hybrid Grounded Systems. For HRG systems the 889

employes a unique combination of Auxiliary Overvoltage and 3rd

Harmonic Neutral Undervoltage protection elements to provide

secure, reliable protection of the stator winding. With this function

the 3rd harmonic neutral voltage variations do not need to be

considered, simplifying the settings and configuration process.

For LRG systems with parallel machines, the 889 provides ground

fault coordination ensuring only the faulted generator is islanded.

In Hybrid Grounded Systems, the 889 provides fast, dynamic

switching from low-z to high-z when an internal generator fault

is detected, reducing potential damage to the generator and

eliminating the need for additional protection devices.

Overall Generator & Transformer Differential Protection

The 889 provides overall generator and transformer differential

protection (87O). It covers the protection zones from the generator

neutral to the Generator Step-Up (GSU) Transformer’s High

Voltage (HV) winding. For mid to large-size machines, the typical

protection philosophy and architecture is to implement a dedicated

transformer protection device along with a single function

differential relay to provide the overall differential protection

between the transformer and the generator. With support for 3

sets of phase CT inputs, the 889 can replace the single function

device, providing the necessary overall differential protection

with the added benefit of protection redundancy for both the

Transformer and the Generator, when there is no tapping between

the generator and GSU or unit transformer.

Generator Stator Differential

The 889 provides fault clearing operation at up to sub-cycle speed,

by utilizing a high-speed dual slope differential protection for

detecting and clearing of stator phase faults. Advanced CT saturation

detection algorithms maintain immunity to saturation conditions that

may be caused due to external disturbances. Through the use of

a directional check, additional supervision is provided to ensure

the fault is internal to the generator before triggering it to trip. This

sub-cycle operation translates to less burning, and hence low carbon

dissipation and thermal stress on insulation. This also enables root

cause analysis during diagnosis/maintenance of the winding (sever

longer duration faults burns-out all the evidence and make root

cause analysis extremely difficult or sometimes impossible).

Applications

• Comprehensive protection from small to large generators

• Industrial or utility power generation

• Co-generation and renewable generation applications

• Unit Transformer Protection applications

Protection & Control

The Multilin 8 Series provides comprehensive and field proven

algorithms to ensure asset management and uninterrupted

process and system availability. With a fast protection pass, the

8 Series relays provide fast operating current, voltage, power, and

frequency protection elements. With highly configurable protection

logic, system coordination with upstream and downstream

disconnect devices is greatly simplified. Various forms of I/O

are supported in the 8 Series to ensure protection, control, and

management of critical substation and field assets.