GE Multilin 869 Overview

Multilin 869 Overview

The Multilin 869 Motor Protection System is a protection device

designed for the management, protection and control of medium to large

horsepower motors. The 869 provides comprehensive protection and

control of various types of motors with different loads they run.

Protection & Control

As part of the 8 Series family, the Multilin 869 provides superior protection

and control. The 869 offers comprehensive protection and control solutions

for medium and large motors for various applications. It contains a full range

of selectively enabled, self contained protection and control elements.

Recent enhancements include the following:

Starting Control

• Start sequence control

• Reluctance torque synchronization

• Incomplete start sequence

• Stabilizing feature

• Auto loading and unloading feature

Squirrel Cage Rotor Thermal Protection (separate from the main

thermal model)

• Time vs speed curve based

• Reduced voltage starting feature

Enhanced Thermal Protection with Speed Biasing

Enhanced power factor protection

• Ride-through feature - directly trips motor

• Resynchronization feature - allows motor to re-synchronize instead of

tripping

Power Factor Based Regulation

Motor Thermal Model

Many motor failures are directly or indirectly related to, or caused

by, extensive heating of the different motor parts involved in

electromechanical operation. Proven through several generations of GE’s

Multilin motor relays, an enhanced thermal model is used in the 869 relay

with seven major features:

Motor thermal limit curves - NEMA® standard, voltage dependent and

customized motor curves

• IEC 60255-8 thermal overload curves

• Smoothing filter for cyclic loads

• Current unbalance biasing

• Independent running and stopped exponential cooling curves

• Optional RTD biasing of the thermal model to adapt to real-time

temperature measurements

• Compensation for hot/cold motor condition

The flexibility of the Multilin 869 thermal models allows for proper set up

and performance for applications, including high inertia and cyclic loads.

Thermal Model with Speed Biasing

This feature acts as an additional check of the amortisseur, or squirrel

cage winding rotor heating. This feature uses estimated speed-dependent

thermal capacity used (actual value ‘’ and compares this value to the

Thermal Capacity Used calculated by the current-based and RTD Bias

(when Enabled) methods. The larger of the three values is used from that

point onward.

RTD Biasing

The Multilin 869 supports up to 13 programmable RTD inputs that can

be configured for an Alarm or Trip. The RTD voting option gives additional

reliability to ignore any RTD failures.

The RTDs can be assigned to a group for monitoring the stator, bearing and

ambient temperatures.

The Thermal Model is also biased by the RTD’s temperature feedback. This

feature allows the relay to protect the motor against unusual high ambient

temperatures or abnormal heating due to overvoltage or damaged

bearings. The RTD biasing feature can correct for this temperature rising

by forcing the TCU register up to the value appropriate to the temperature

of the hottest stator RTD.

High-Inertia Load Applications

The voltage dependent overload curve feature in Thermal Model is

tailored to protect motors which are used in high inertia load applications.

Voltage is continually monitored when the motor is started and during

acceleration. The thermal limit curve is then adjusted accordingly. This

enables the Multilin 869 to distinguish between a locked rotor condition,

an accelerating condition and a running condition.

VFD-Driven Motor Applications

The Multilin 869 provides protection for motors fed through VFDs (Variable

Frequency Drives). A wide range of the frequency tracking (3-72Hz) allows

the 869 to track the motor frequency and adjust its sampling rate to

accurately measure phasors. An advanced algorithm allows switchable

current and voltage tracking in case VFD is bypassed.

Thermal protection also considers the extra heating generated by the

higher harmonics due to VFD to achieve the accurate response to the

actual motor heating. RMS currents fed to the various motor protection

elements are further processed through the averaging filter to eliminate

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.

The start sequence function is comprised of three field application

control methodologies:

- Slip-frequency based for brush-type motor applications.

- Timer-based for both brushless and brush-type motor applications.

- Reluctance-torque based synchronization for brush-type motor applications.

• Incomplete start sequence protection to trip/alarm if the starting

sequence is not completed within a set time.

• Load application relay functionality enabling motor loading following

the DC field application and unloading following a trip and/or loss of

synchronization (pole slipping).

• Start sequence control when the motor enters re-synchronization mode.