Generator Test Rig For Aircraft Starter generator
Technical Field:
The invention is related to the conceptualization and design of a universal Test Rig meant
for testing of generator function of Aircraft Starter Generator and other aircraft
accessories viz., Voltage Regulator, Single Pole Single Throw (SPST) Contactor, Reverse
Current Relay and Circuit Breakers.
Background:
Starter Generator is a primary part of an aircraft for starting of the Aircraft Engine and
generating DC electrical supply to aircraft and for charging of aircraft battery. It draws
power from the aircraft battery and initially works as Starter motor driving the Engine.
When the Engine attains specific speed after starting, the Starter Generator starts
functioning as Generator. It is rotated by the Aircraft Engine and starts supplying Electrical
Power to the aircraft. The aircraft electrical system incorporates four other electrical
accessories also viz., (a) SPST Contactor, (b) Reverse Current Relay, (c) Voltage Regulator
and (d) Circuit Breakers, among others. These electrical accessories play crucial role in
supply of electrical current and reversal of role of the Starter Generator from Starter to
Generator.
The invention is aimed at design and setting up of a combined Test Rig meant for testing
the Generator of Artouste 1MB Engine, which is installed in Cheetah and Chetak
Helicopters (licensed version of 'Alouette' & 'Lama' Helicopters) and four other accessories
of Helicopters, as mentioned above, on a single Test Rig.

Description
The Test Rig is capable of testing Generator function of a Starter Generator, which senses
and reveal initial voltage production with respect to shaft speed and capacity of the
generator to sustain desired load as per specification.
In addition to the Generator, the Test Rig is also capable of testing Voltage Regulator,
SPST contactor, Reverse Current Relay and Circuit Breakers (1A to 25A) in conjunction
with a Generator installed on the Test Rig.
Test Set UP:
The Test Rig set-up is explained in Fig.1. The Test Bench is depicted at (7), where Gear Box
(3) is coupled with the 3-phase Squirrel Cage Induction Motor 11KW, 415V (1) through the
coupling (2). The Starter Generator under test is mounted on a fixture and is aligned with
the shaft of the Gear Box through Alignment Fixture (4). The Gear Box is cooled by oil
pumped from a Tank (13) under the Test Bench. Starter Generator under test is cooled by
air blown through a hose (6) from a blower underneath. The Test Bench is powered from
the Electrical Switch Gear and Drive Panel (12).
The Test Rig consists of the following major modules-
1. Test Bench, on which a 3-phase Squirrel Cage Induction Motor 11KW, 415V (1)
with Gear Box (3) and allied accessories.
2. Display Panel (8) with different Ammeters, Voltmeters, RPM Gauge etc.
3. Electrical Load Bank (11).
4. Electrical Switch Gear and Drive Panel (12).
The induction motor is the prime mover that drives the generator. The generator output
is connected to the display panel (8) for display of its various parameters.

As the Generator is driven by the motor (1), the RPM of the shaft, voltage generated and
DC current supply to the electrical load is measured and displayed in the Display Panel (8).
The RPM of the Induction motor can be varied by varying voltage and frequency of the AC
input. The electrical load is applied to the Generator output through the Electrical Load
Bank (11). The load can be varied through a combination of Load Selectors in the Load
Bank and fine tuned by Rheostats. The performance of the Generator in respect of RPM,
voltage and current is tabulated. The measured values are compared with desired
characteristics and test acceptability of the Starter Generator is determined.
The Voltage Regulator is mounted on a fixture (9) on top of the Display Panel (8) and
connected with the generator. The generator speed can be varied through variation of
speed of prime mover by a tuner on the Display Panel. The Voltage Regulator under test is
tested at different load at different Generator speed. The Voltage output range of the
Generator and its stability is also determined alongwith specific value of the voltage
where the voltage drop is minimum on application of load. The result is compared with
desired value of the Voltage Regulator and the test acceptability determined.
The Reverse Current Relay (10) is placed between the Generator positive terminal of the
Test Rig and positive terminal of an external battery source similar to one used in Aircraft.
In this Test Rig we can test the parameters related to the main contacts of the Reverse
Current Relay. As the Generator voltage gradually increases and exceeds the Battery
voltage by a preset value, the relay closes allowing the battery to be charged. In this
condition, electrical load is applied through load selection switches of the rig and voltage
drop between the Generator & Battery terminals is displayed for the specific load. During
switching off of the generator, as the Generator voltage falls below the Battery voltage,
the Reverse Current Relay disallows reverse flow of the current towards Generator field
for a certain set value of the reverse current and the said current value appears in the
digital ammeter of the Test Rig with negative value.

The testing of SPST Contactors through the rig is similar to the RC Relay. 1 & 2, the main
terminals connect the Generator positive and the battery source. By means of another DC
source from the rig applying to 3 & 4 terminals the contactor closes. Now on application
of certain load similar to that exerted in the aircraft, the voltage drop needs to be
checked. The result is compared with the desired value
The Circuit Breakers (CB) need to be checked applying about double the rated current
by placing them between the same terminals like the previous units and the required load
is applied on them by selecting the proper load switch and it is checked if the CB is
tripping and disconnecting the circuit within a stipulated time and under stipulated
voltage.

Generator Test Rig For Aircraft Starter generator
CLAIM
What is claimed is:
1.0 A combined Test Rig useful for performance test of generator function of Starter
Generator of an aircraft and its accessories viz., Reverse Current Relay, Voltage
Stabiliser, SPST Contactor and Circuit Breaker.
2.0 Test Rig as claimed in Claim 1.0 is capable of testing the Generator in conjunction
with Voltage Regulator as claimed in Claim 1.0.
3.0 Test Rig as claimed in Claim 1.0 is capable of testing the performance of the
accessories as claimed in Claim 1.0 in conjunction with the Starter Generator
mounted and connected in the invented Test Rig..
4.0 Test Rig as claimed in Claim 1.0 has 4 nos. of main Modules
4.1 Test Bench
4.2 Display Panel
4.3 Electrical Load Bank
4.4 Electrical Switch Gear & Drive Panel.
5.0 The modular feature as claimed in Claim 4.0 facilitates ease of maintenance.
6.0 Test Rig as claimed in Claim 1.0 is specifically designed for tarter Generators of
Cheetah & Chetak Helicopters, but can be adapted to other aircraft Starter
Generators with variation in design and capacity of the modules.