Power Plant Engineering

9.6 AUXILIARY SYSTEMS
Auxiliary systems are the backbone of the gas turbine plant. Without auxiliary system, the very
existence of the gas turbine is impossible. It permits the safe working of the gas turbine. The auxiliary
system includes starting, ignition, lubrication and fuel system and control.
9.6.1 STARTING SYSTEMS
Two separate systems-starting and ignition are required to ensure a gas turbine engine will start
satisfactorily. During engine starting the two systems must operate simultaneously.
9.6.1.1 Types of Starter
The following are the various types of gas turbine starter.
(a) Electrical
(i) A.C. and (ii) D.C.
A.C. cranking motors are usually 3 phase induction types rated to operate on the available volt-
age and frequency.
D.C. starter motor takes the source of electrical energy from a bank of batteries of sufficient
capacity to handle the starting load. Engaging or disengaging clutch is used.
(b) Pneumatic or Air Starter. Air starting is used mostly as it is light, simple and economical to
operate. As air starter motor has a turbine rotor that transmits power through a reduction gear and clutch
to the starter output shaft that is connected to the engine. The starter turbine is rotated by air pressure
taken from an external ground supply, from an auxiliary power unit carried in the aircraft or from an
engine that is running. An electrical control unit controls the air supply to the starter by opening the
pressure-reducing valve. When an engine starter is selected and is automatically closed at a predeter-
mined starter speed the clutch also automatically disengages as the engine accelerates. It is most suitable
for natural gas pipeline gas turbine drive.
(c) Combustion Starter. It is in every respect a small gas turbine. It is a completely integrated
system which incorporates a planetary reduction gear drive with over-running clutch. The unit is started
with the electric starter. The starter turbine is directly geared to the gas turbine shaft through a reduction
gear.

---

GAS TURBINE POWER PLANT
283