GE Multilin 869 Overview

oscillations in current signals to ensure the security.

Additionally, users may indicate a  starting  VFD  frequency  that  helps

the device to track the motor frequency faster and therefore accurately

measures the phasor quantities, which, otherwise, could cause delayed or

false protection operation of the protection.

Cyclic Load Motor Applications

Input currents of a motor driving  cyclic  load  can vary between very low

to above the maximum allowable current during a load cycle. Variation in

current magnitude results in motor heating and cooling depending on the

heat and cooling time constants. Thermal overload protection response

is made adaptive to the cyclic load based on the cooling time constants.

In addition, to provide more accurate overload thermal model response

to cyclic load, the input currents to the thermal model are averaged over

the settable duty cycle interval. With a reciprocating load application, the

number of cycles to average can be determined from current waveform

capture using the Oscillography/Datalogger features in the 869 motor

protection relay.

Synchronous Motor Applications

The 869 is equipped to protect and control synchronous machines

without the need for external hardware. All protection functions essential

to the synchronous motor during asynchronous operation while starting

up, during normal and overload operations and under fault conditions

are available. In addition to stator  protection and control, the relay

provides protection and monitoring of exciting rotor during pull-out or

loss of synchronism condition with elements like Out-of-Step, Loss-of

Field, Reactive Power, and Power Factor. With its well established and

matured Thermal Model, it prevents overheating of both stator and rotor

windings during both synchronous and asynchronous operation. During

asynchronous operation or startup, the thermal model with VD (voltage

dependent) function provides protection against excessive heating in the

damper winding due to stalled or locked rotor conditions.

SM Field Overcurrent/ Undercurrent

The 869 relay provides monitoring of overcurrent and loss of DC field

excitation input to the rotor of a synchronous motor. These elements

respond to DC current input from the direct current transducer.

SM Field Overtemperature

The 869 relay provides protection of the rotor winding against overheating

by exploiting the direct proportionality between temperature and

resistance. This elements responds to rotor resistance to detect rotor

temperature. When magnitude of the field resistance or temperature

exceeds the Pickup level for the time specified by the Pickup Delay setting.

SM Field Overvoltage/ Undervoltage

Excitation system output voltage to the rotor is monitored using these

elements, corresponding to DC Field voltage measured across the field

winding or exciter terminals. DC voltage is brought to the relay terminals

through the voltage divider network, provided with the relay.

SM PF Regulation

Power Factor (PF) regulation is useful in applications where motors are

subjected to high-level transient impact loads (such as chipper drives).

The PF regulator senses the power factor dip occurring when the motor

is loaded and signals the silicon-controlled rectifier (SCR) Exciter to

respond with a boosted output. As a result, the pull-out torque of the

synchronous motor is increased for the duration of the transient load.

After the load subsides, the regulator senses an excessive leading power

factor and signals the SCR to reduce its output. This automatic boosting

of field current to avoid pull-out is called field forcing. The Power Factor

regulator thus provides automatic boosting when field forcing is required

and economical low field operation when the motor is idling.

Another application of the power factor regulator is to control power

factor swings resulting from various levels of loading so as not to cause

fluctuations in the plant system voltage.

SM Start Sequence Control

The 869 Start Sequence Control function provides:

• Controlled application of a DC field to the rotor winding for both brush

type and brushless synchronous motors.