Protection; Thermal Protection; Temperature Limits For The Windings; Thermal Protection For The Bearings - WEG G Serie Manual De Instalación, Operación Y Mantenimiento

4.6 PROTECTION

4.6.1 Thermal protection

Alternators have, when requested by the client, protective
devices against excessive rise in temperature, installed in the
stator coils, and / or bearings, as follows:
Thermostat (bimetal): bimetallic thermal detectors, with
normally closed silver contacts that open when they reach
the temperature of operation. Thermostats can be
connected in series or independently according to wiring
diagram.
Thermistors (PTC or NTC type): Heat detectors,
semiconductor compounds that vary their resistance sharply
to reach the temperature of operation. Thermistors can be
connected in series or independently according to wiring
diagram.
NOTE
Thermostats and thermistors must be
connected to a control unit that stops operation
of the alternator or triggers a signaling device.
Thermistor (RTD) - A calibrated resistance element. Its
operation is based on the principle that the electrical
resistance of a metallic conductor varies linearly with
temperature. The terminals of the detector must be
connected to a control panel which includes a temperature
gauge.
NOTE
The thermistors type RTD allow monitoring of
the absolute temperature. With this information,
the relay can do the temperature reading, as
well as the parameterization for alarm and
shutdown according to the preset
temperatures.
The following formula is used to convert the value of the
ohmic resistance of the temperature measurement for
thermistors Type Pt 100.
Formula:  - 100 = C
0,386
Where:  = ohmic resistance measured on the PT-100
The protective devices, when requested, are listed in the
wiring diagram specific to each alternator. The non-use of
these devices is the sole responsibility of the user, but may
result in loss of guarantee in case of damage.
4.6.1.1

Temperature limits for the windings

The temperature of the hottest point of the winding must be
kept below the limit of thermal class of insulation. The total
temperature is composed of the sum of temperature with
the rise of temperature (T), plus the difference between the
average temperature of the winding and the hottest point of
the winding. The ambient temperature is typically up to 40
°C. Above this value, the working conditions are considered
special.
10680382 Installation, operation and maintenance manual – Synchronous Alternator – G line - Horizontal
Table 4.5 shows the numerical values and composition of
the permitted temperature of the hottest point of the
winding.
Table 4.5: Insulation class
Insulation class
Ambient temperature
T = temperature rise (resistance method)
Difference between the hottest point and the
average temperature
Total: Temperature of the hottest point
ATTENTION
If the alternator works with winding
temperatures above the limits of thermal
class, the life of the insulation and hence of
the alternator is reduced substantially, or
even may cause burning of the alternator.

4.6.1.2 Thermal protection for the bearings

The temperature sensors installed on the bearings (if any)
are used to protect them from damage due to operation
with overheating.

4.6.1.3 Temperatures for alarm and shutdown

Temperature of alarm and shutdown must be
parameterized as low as possible. These temperatures
can be determined based on the results of tests or by
operating temperature of the alternator.
The temperature alarm can be set to 10°C above the
operating temperature of the alternator at full load
considering the highest ambient temperature at the
location. The temperature set to shutdown shall not
exceed the maximum permitted temperatures as listed in
Table 4.6 and Table 4.7.
Table 4.6: Maximum temperature of stator - continuous duty
STATOR WINDING
Class
of Insulation
F
H
ATTENTION
Alternators used in emergency systems
(standby) can be elevated up to 25 º C above
the temperature in continuous operation as
standard NEMA MG 1 and MG-22:40-1-
22.84. Using the alternator in these
conditions reduces the life of the alternator.
www.weg.net
F
°C 40
°C 105 125
°C 10
°C 155 180
Maximum temperature of
protection setting (ºC)
Alarm Shutdown
140 155
155 180
l 25
H
40
15