Stamford MX341 - User Manual

MX341 AUTOMATIC VOLTAGE
REGULATOR (AVR)
SPECIFICATION, INSTALLATION AND ADJUSTMENTS
GENERAL DESCRIPTION
The MX341 is a two phase sensed Automatic Voltage
Regulator (AVR) and forms part of the excitation system for a
brushless generator.
In addition to regulating the generator voltage, the AVR
circuitry includes protective features to ensure safe reliable
control of the generator. Excitation power is derived from a
permanent magnet generator (PMG) to guarantee low Radio
Frequency Interference (RFI) and immunity from thyristor type
loads.
The AVR is linked with the main stator windings and controls
the power fed to the exciter stator and hence the main rotor to
maintain the machine output voltage within the specified
limits, compensating for load, speed, temperature and power
factor of the generator.
Soft start circuitry is included to provide a smooth controlled
build up of generator output voltage.
A frequency measuring circuit continually monitors the shaft
speed of the generator and provides underspeed protection of
the excitation system by reducing the generator output
voltage proportionally with speed below a presettable
threshold. A further enhancement of this feature is an
adjustable volts/Hz slope to improve frequency recovery time
on turbo charged engines.
Uncontrolled over excitation is limited to a safe period by
internal shutdown of the AVR output device. This condition
remains latched until the generator has been stopped.
Provision is made for the connection of a remote voltage
trimmer allowing the user fine control of the generator's
output.
Accessories are available for this AVR. Please refer to factory
for further details.
TECHNICAL SPECIFICATION
SENSING INPUT
Voltage 170-250 V ac max
Frequency 50-60 Hz nominal
Phase 2
Wire 2
POWER INPUT (PMG)
Voltage 140-220 V ac
Current 3 A/phase
Frequency 100-120 Hz nominal
Phase 3
Wire 3
OUTPUT
Voltage max 120 V dc
Current continuous 2.7 A
Transient 6 A for 10 seconds
Field Resistance 15
Ω
minimum
REGULATION (See Note 1) +/- 1%
THERMAL DRIFT
(after 10 min)
1% for 40°C change in AVR ambient
SOFT START RAMP TIME
3 seconds
TYPICAL SYSTEM RESPONSE
Field current to 90% 80ms
Machine Volts to 97% 300ms
EXTERNAL VOLTAGE ADJUSTMENT
+/- 6% with 1 K
Ω
trimmer
UNDER FREQUENCY PROTECTION
Set Point (see note 2) 95% Hz
Slope 100-300% down to 30 Hz
UNIT POWER DISSIPATION
12 watts maximum
ACCESSORY INPUT
+/- 1 V = +/- 5% change in output volts
QUADRATURE DROOP
Maximum sensitivity (10
Ω
Burden)
0.07A for 5% droop @ 0p.f.
OVER EXCITATION PROTECTION
Set Point 75 V dc
Time Delay (fixed) 10 seconds
ENVIRONMENTAL
Vibration 20-100Hz 50mm/sec
100Hz-2 kHz 3.3g
Relative Humidity 0-60°C 95%
Operating Temperature -40°C to + 70°C
Storage Temperature -55°C + 80°C
NOTES
1. With 4% engine governing
2. Factory set, semi-sealed, jumper selectable.

Summary

General Description of MX341 AVR

MX341 AVR Functionality

Details the MX341 as a two-phase sensed Automatic Voltage Regulator for brushless generators, including protective features.

Excitation Power Source and RFI Immunity

Explains excitation power derivation from a PMG for low RFI and immunity to thyristor loads.

Voltage Regulation Mechanism

Describes how the AVR links with stator windings to control power to the exciter stator for voltage maintenance.

Soft Start and Frequency Measurement Features

Highlights soft start circuitry for smooth voltage build-up and frequency measurement for underspeed protection.

Over Excitation Protection and Remote Trimmer

Details limited over excitation shutdown and provision for a remote voltage trimmer.

MX341 AVR Technical Specifications Overview

Sensing Input Specifications

Specifies voltage, frequency, phase, and wire configuration for sensing input.

Power Input (PMG) Specifications

Details voltage, current, frequency, phase, and wire for the PMG power input.

Output Specifications

Lists maximum voltage, continuous and transient current, and minimum field resistance.

Regulation and Thermal Drift

Specifies regulation accuracy and thermal drift percentage per degree Celsius change.

Soft Start and System Response

Details soft start ramp time and typical system response for field current and machine volts.

Protection and Dissipation Specs

Covers external voltage adjustment, under frequency protection, power dissipation, and accessory input.

Droop and Over Excitation Protection

Specifies quadrature droop sensitivity and over excitation protection set point and delay.

Environmental and Notes

Details vibration, humidity, operating/storage temperatures, and notes on engine governing.

MX341 AVR Design Details and Functions

Sensing Resistors Function

Explains how sensing resistors attenuate generator output voltage and allow adjustment.

Quadrature Droop Circuit Function

Describes the droop circuit's role in reactive load sharing for paralleled generators.

Offset Control and Power Supply

Details offset control for accessories and power supply components for integrated circuits.

Precision Voltage Reference and Soft Start

Explains the stable voltage reference and the soft start circuit for gradual voltage increase.

Comparator, Stability, and Power Control

Describes the comparator, stability circuit for performance, and power control driver.

Power Control Devices and Synchronizing Circuit

Explains power control devices for exciter current and the synchronizing circuit's function.

Under Frequency Roll Off (UFRO) Circuit

Details the UFRO circuit for underspeed protection and its LED indicator.

Engine Relief and Overload Detector

Explains engine relief for load acceptance and overload detection for shutdown.

Fitting and Operating the MX341 AVR

AVR Control Summary

Summarizes the function and direction of control adjustments like VOLTS, STABILITY, UFRO, and DROOP.

Voltage Adjustment Procedure

Provides a step-by-step guide for adjusting the generator output voltage.

Warning on Voltage Adjustment

Caution against exceeding rated generator voltage and advises consulting the rating plate.

MX341 AVR Adjustments and Settings

Stability Adjustment Guide

Explains how to adjust the stability control for optimal steady state and transient performance.

Optimum Response Selection

Details the use of jumper selector leads for matching AVR to generator frame size.

Under Frequency Roll Off (UFRO) Adjustment

Describes UFRO adjustment for underspeed protection and LED indication.

DIP Adjustment for Load Dip

Explains the DIP adjustment for controlling generator voltage dip on load application, especially for turbo-charged engines.

Droop Adjustment

Details droop adjustment for parallel operation using a quadrature droop CT.

Trim Adjustment (V;TRIM)

Explains the auxiliary input for connecting to VPF controllers and adjusting sensitivity.

Over Excitation (EXC TRIP) Adjustment

Notes that EXC TRIP adjustment is factory set and sealed, indicating over excitation and underspeed.

Stamford MX341 Specifications

General

Brand	Stamford
Model	MX341
Category	Controller
Language	English