2. DESCRIPTION OF SUB-ASSEMBLIES
2.1 STATOR
2.1.1 Electric machine armature
The alternator stator (armature) is a stacking of low losses
steel laminations assembled under pressure. The stator
coils are inserted and blocked in the slots, then
impregnated with varnish and polymerised (VPI system).
1 - Stator
2 - Rotor
3 - Exciter
4 - Rotating diodes
5 - Fan
a - Stator Air inlet (cold air)
b - Stator air exhaust (warmed air)
c – Rotating diodes air cooling
2.1.2 Excitation field winding
The excitation field winding comprises a wound solid
element.
The excitation is flanged on the rear end shield of the
machine.
2.1.3 Stator protection
2.1.3.1 Heating resistor
The heating element avoids internal condensation during
the shutdown periods. It is connected to the main terminal
box strip. The heating resistor is switched on as soon as
the machine is shut down.
The electrical characteristics are provided in Section 1
"Technical Characteristics".
2.1.3.2 Stator winding temperature sensor
The temperature sensors are located in the zone assumed
to be the hottest part of the machine. The sensors are
connected to a terminal box.
Depending on the temperature rise of the machine, the
temperature of the sensors should not exceed a maximum
of :
TEMP. RISE
class
ALARM TRIP
Power (KVA) < 5000 > 5000 < 5000 > 5000
130 °C 125 °C 135 °C 130 °C
155 °C 150 °C 160 °C 155 °C
H
175 °C 170 °C 180 °C 175 °C
To improve the machine protection we recommend to set
the alarm point following effective site conditions:
Alarm temperature (*) = Highest recorded temp + 10°K
Trip temperature (*) = Alarm temperature + 5 °K
(*) do not pass over the values of the previous table.
(*)Highest recorded temp: Temperature measured at
the site in the worst temperature condition at the stator
temperature sensor
E.g.: a class B machine (3000 kVA) reached 110°C during
a factory heat run test. Set the alarm temperature to 120°C
instead of 130°C as indicated in the previous chart. Set the
emergency shutdown to 125°C instead of 135°C as
indicated in the previous chart.
2.1.3.3 Stator air sensor
As an option an RTD or thermostat can measure the stator
air inlet temperature (cold air)
Stator air inlet temperature; Alarm points and shutdown:
• alarm Nominal air inlet stator + 5 K
• shutdown 80°C
Stator air outlet temperature; Alarm points and shutdown:
• alarm Nominal air inlet stator + 35K
• shutdown Nominal air inlet stator + 40K
NOTE :
For an open drip proof machine the nominal air
temperature entering the stator corresponds to the ambiant
temperature
NOTE :
If quickly restarting after a stop Inhibit the stator air sensor
safety "alarm" for few seconds (no more than 30 s) during
the machine start up;
NOTE:
For a water cooled machine (CACW) the nominal air
entering the stator may be approximated as following:
Tair entering stator = Twater entering cooler + 15°K
E
lectric Power Generation
Installation and maintenance
5654 en - 2017.10 / a
LSA 52.2 MHV
Industrial Range Alternators - 4 pole
6
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