Category: GE

Description of the 889 Generator Protection System

CPU

Relay functions are controlled by two processors: a Freescale MPC5125 32-bit

microprocessor that measures all analog signals and digital inputs and controls all output

relays, and a Freescale MPC8358 32-bit microprocessor that controls all the advanced

Ethernet communication protocols.

Analog Input and Waveform Capture

Magnetic transformers are used to scale-down the incoming analog signals from the

source instrument transformers. The analog signals are then passed through a 11.5 kHz

low pass analog anti-aliasing filter. All signals are then simultaneously captured by sample

and hold buffers to ensure there are no phase shifts. The signals are converted to digital

values by a 16-bit A/D converter before finally being passed on to the CPU for analysis.

The ‘raw’ samples are scaled in software, then placed into the waveform capture buffer,

thus emulating a digital fault recorder. The waveforms can be retrieved from the relay via

the EnerVista 8 Series Setup software for display and diagnostics.

Frequency

Frequency measurement is accomplished by measuring the time between zero crossings

of the composite signal of three-phase bus voltages, line voltage or three-phase currents.

The signals are passed through a low pass filter to prevent false zero crossings. Frequency

tracking utilizes the measured frequency to set the sampling rate for current and voltage

which results in better accuracy for the Discrete Fourier Transform (DFT) algorithm for offnominal

frequencies.

Overview

The relay features generator unbalance, generator differential, over excitation, loss of

excitation, 3rd harmonic neutral undervoltage, over and under frequency, synchrocheck

and other essential functions with a basic order option. Additionally available with an

advanced order option are overall differential (to protect the transformer-generator

combined), directional overcurrent elements, restricted ground fault, 100% stator ground,

out-of-step protection, rate of change of frequency, power factor, harmonic detection,

frequency out-of-band accumulation and others. An optional RTD module allows for

thermal protection and monitoring. An optional analog inputs/outputs module allows for

monitoring of generator excitation current, vibration and other parameters.

These relays contain many innovative features. To meet diverse utility standards and

industry requirements, these features have the flexibility to be programmed to meet

specific user needs. This flexibility will naturally make a piece of equipment difficult to

learn. To aid new users in getting basic protection operating quickly, setpoints are set to

typical default values and advanced features are disabled. These settings can be

reprogrammed at any time.

Programming can be accomplished with the front panel keys and display. Due to the

numerous settings, this manual method can be somewhat laborious. To simplify

programming and provide a more intuitive interface, setpoints can be entered with a PC

running the EnerVista 8 Setup software provided with the relay. Even with minimal

computer knowledge, this menu-driven software provides easy access to all front panel

functions. Actual values and setpoints can be displayed, altered, stored, and printed. If

settings are stored in a setpoint file, they can be downloaded at any time to the front panel

program port of the relay via a computer cable connected to the USB port of any personal

computer.

Introduction

The GE Multilin 515 Blocking and Test Module has the following features:

• 14 Pole switchbank

• CT inputs short when current switches are opened

• Current injection for each phase

• Ground terminal

• Ability to visually isolate (open) trip relay output circuits

• Cover provided

• Suitable for utility and industrial use

• 515 test plugs available

Description

The 515 Blocking and Test Module provides an effective means of trip blocking, relay isolation and testing of GE Multilin relays. By opening the switches and inserting test plugs, phase and residual currents from the primary CTs can be monitored. Currents can be injected into the relay from a secondary injection test set during commissioning.

Prior to testing, the trip and auxiliary circuits must first be opened to prevent nuisance tripping; CTs can then be shorted. Conversely, when the test is complete and the relay put back into operation, the CT switches should be closed first to ensure normal operation of the relay, prior to closing the trip and auxiliary circuits.

Installation

Shorting switches are provided for connection of 3 phase CTs (current transformers) and a separate core balance ground fault CT or 3 phase CTs connected for residual ground fault sensing.

When each CT switch is opened, the CT is shorted. It is essential that the CT is connected to the shorted side of the switch as shown in the following figure, otherwise dangerously high voltages would be present from the open circuited CTs.

When the switches are open, test plugs can be inserted to either inject signals into the relay wired to the switches or monitor signals such as CT current from the switchgear.

The 515 Blocking and Test Module consists of a metal chassis attached to the 515 test switches that slides into the panel. A single cutout in the panel, as per the dimensions shown in Figure 3, is required to mount the 515 test switches.

DESIGN CHARACTERISTICS

Measurement accuracy

The differential angle measurement of the MLJ is high precision and is limited solely by errors in available

voltage transformers.

The measurement of the angle is practically independent of the voltage.

In the MLJ the measurement is obtained via a numerical calculation done on digital voltage samples, thus

achieving high precision. This allows for a rating of 2º, which is clearly better than the possible rating using

other technologies.

Influence of harmonics

The pillar of the MLJ measurement calculation is the discrete Fourier transform, which is in essence a

harmonics filter. For this reason the voltage and line measurements are not affected by frequencies other

than the fundamental.

The rejection of harmonics is added to the independence of measurements, both magnitude and phase,

relative to frequency signal variations, which is very important in a synchronism checking relay which, by its

own nature, works in variable frequencies.

Given that in power systems, synchronization or synchronism checking is carried out in a steady state, that

is with voltage magnitudes near or equal to the rated value, close enable is not emitted for very low voltages.

Therefore, for voltage of less than 9 volts, the relay stops measuring phase and frequency, not giving

permission to close under such conditions.

The MLJ also offers additional insensitivity to frequency measurement concerning harmonics, since this is

done via a hardware circuit, a zero-cross detector, with an intrinsic harmonics filter. Furthermore, it has a

software filter which operates by double-period measurement, both between the rising and falling edges,

averaging them out and allowing for better performance of algorithm frequency (improving security and

response).

DESCRIPTION

The main applications of the MLJ are:
• Connecting a generator to the system.
• Re-establishing the connection between two parts of the system.
• Manual closing of circuit breakers
• Automatic reclosing of a breaker after a relay trip.
The MLJ is a digital synchronism-checking relay that measures bus and line voltages.

It tests:
• Voltage difference
• Frequency slip
• The phase angle between both voltages
The equipment provides an output to enable to close the circuit breaker when all of the values fall within the set limits and remain there for the duration of time chosen for the setting. In the event that all the conditions have not been met, after one minute the equipment gives off a signal showing a failure of closing conditions.
The relay functions in two modes:
• Continuous mode: In this mode synchronism is checked continuously.
• Manual mode: This is activated when voltage is applied through a manually activated input, thus
beginning synchronism control when voltage applied through another digital input for initial checking.

The IC670MDL331 is a field control I/O module manufactured by GE Fanuc. The module is a discrete output module with eight (8) channels in four (4) groups of two (2) channels each. It provides an output voltage range of 85-132 VAC, a nominal output of 120 VAC, and a maximum output current of 2 A per channel.The module has a backplane current consumption of 154 mA.

About the IC670MDL331

This IC670MDL331 is manufactured by GE Fanuc and is part of the Field Control family. It is an I/O module, specifically, a discrete output module with eight (8) output channels divided into four (4) with two (2) channels each. It provides an output voltage of 85-132 VAC, 47-63 Hz, and a nominal output level of 120 VAC.Each channel of the module is designed to provide a maximum output current of 2 amps, making the module compatible with inductive loads.

Although the IC670MDL331 is rated for 2 A per channel, the maximum output per group is limited to a maximum of 2 A. Additionally, the maximum output per module is limited to 6A – 8 A. The module is equipped with LED status indicators, such as Logic Side Indicators, describing the on and off status of each channel, and Fuse OK LEDs, indicating the status of the fuses mounted inside each channel group. status of the fuses installed inside each channel group.

The IC670MDL331 is used in conjunction with a Bus Interface Unit (BIU). This BIU sends individual channel status to a host controller that resides on a protocol supported by the BIU. In addition, the controller can access the diagnostic status of the IC670MDL331 through the BIU.

Power Sources

The module receives power from the Field Processor to run its own 5–volt logic. An external

24VDC supply is needed to power the input devices.

LEDs

Individual LEDs (logic side), visible through the transparent portion of the module top,

indicate the on/off status of each input. The PWR LED is on when field and backplane power

are present.

Host Interface

Intelligent processing for this module is performed by the Bus Interface Unit or elsewhere in

the system. This includes configuring features such as input defaults and fault reporting. The

module has 16 bits (two bytes) of discrete input data. A Bus Interface Unit is required to

provide this input data to the host and/or local processor.

Module Operation

A network of resistors and capacitors establishes input thresholds and provides input filtering.

Optoisolators provide isolation between the field inputs and the module’s logic components.

Data from all 16 inputs is placed into a data buffer. The module’s circuit LEDs show the

current states of the 16 inputs in this data buffer.

Parallel–to–seri al converters change input data from the data buffer into the serial format

needed by the Bus Interface Unit.

After checking the Board ID and verifying that the module is receiving appropriate logic power

from the Bus Interface Unit (which is reflected by the state of the module’s Power LED), the Bus

Interface Module then reads the filtered, converted input data.

Power Sources

The module receives power from the Bus Interface Unit for its own operation. An external 48

VDC supply is needed to power the input devices.

LEDs

Individual LEDs (logic side), visible through the transparent portion of the module top,

indicate the On/Off status of each input. The PWR LED is On when field and backplane

power are present.

Host Interface

Intelligent processing for this module is performed by the Bus Interface Unit or elsewhere in

the system. This includes configuring features such as input defaults and fault reporting.

The module has 16 bits (two bytes) of discrete input data. A Bus Interface Unit is required

to provide this input data to the host and/or local processor.

Module Operation

A network of resistors, capacitors, and zener diodes establishes input thresholds and provides

input filtering. Optoisolators provide isolation between the field inputs and the module’s logic

components. An oscillator and switch form a sampling circuit that is transparent to the

controller and the LEDs that indicate the state of the inputs. Data from all 16 inputs is placed

into a data buffer. The module’s circuit LEDs show the current states of the 16 inputs in this

data buffer.

Parallel-to-serial converters change input data from the data buffer into the serial format

needed by the Bus Interface Unit.

This IC670MDL740 is a positive logic discrete output module manufactured by GE Fanuc. The module is a general-purpose output module that is mounted on a Bus Interface Unit (BIU) to implement an extended I/O solution. It is typically used for energised output devices such as indicator lights, relay coils, solenoid driven devices and similar devices with low current ratings because the IC670MDL740 provides 10.30 amps of output current per channel and a total of 24 amps of output current per module over a voltage output range of 0-5 VDC and a nominal voltage of 4 VDC.

The IC670MDL740 is designed with individual status LEDs to indicate the on/off status of each output channel of the module. 

The entire I/O group is fitted with a common fuse that is also assigned an LED to describe the blown fuse status. The module generates an inrush current rated at 2 amps with a maximum duration of 100 ms. The output channels have a minimum load current of 1 mA per point, an output voltage drop of 0.5 V, an output leakage current of 5.30 mA at 0 VDC, and a typical response time for on and off signal transitions.

The IC670MDL740 comes with an integrated terminal block consisting of 25 terminals. Each terminal is designed to terminate one AWG #14 – AWG #22 wire or two (18) wires using AWG #2 wire. By installing external jumpers on this module, the allowable wire size is reduced to AWG #14 to AWG #16.

The Field Control IC670MDL742 DC Negative Output Module is a GE Fanuc 5-, 12-, and 24-volt DC rated output module with 16 negative logic discrete outputs.

The outputs are used as current-sucking outputs to switch the load to the negative side of the DC power supply.Power for the IC670MDL742 DC Negative Output Module is provided by the bus interface module.

It is recommended that an external DC power module be used to provide the power required by the load. The module contains a 10 ampere rated fuse for connection to an external power source.

There is a clear potion on the top of the module for clearly visible LED indicators.

The IC670MDL742 DC Negative Output Module performs processing through the bus interface unit.

The bus interface module also helps to collect output data from a host device or processor.

Its PWR indicator LED can be used to check that the module’s backplane power is present and that the fuse is not blown.

The module’s logic power is received from the Bus Interface Unit. An optoisolator isolates the module’s logic components from the field outputs.

It consists of FETs powered from an external supply to absorb the current flowing through the load.

The outputs are capable of absorbing up to 0.5 amps per point. The total steady-state load for the entire module is 8 amps.

The IC670MDL742 DC Inverting Output Module has one set of outputs and does not provide isolation between points in the set.

It is supplied with an easily removable fuse to protect the outputs from high currents or reversal of power supply polarity.