Generators for C15/C18 Engines Caterpillar


Protective Devices

Usage:

C15 L8B

Thermal protection (By Request)

Generators have optional equipment that is available. Some of the optional equipment includes thermal protection devices that can be installed for stator windings and bearings.

Thermostat (bimetal)

One type of thermal protection is the bimetallic thermostat. The bimetal thermostat contains normally closed silver contacts that open when the contacts reach the temperature of operation. Thermostats can be connected in series or independently.

Thermistors

There are two types of thermistors as follows:

  • Positive Temperature Coefficient (PTC)

  • Negative Temperature Coefficient (NTC)

Thermistors are heat detectors that are made of semiconductor compounds that vary in resistance as the temperature changes. of operation. Thermistors can be connected in series or independently.

Note: Thermostats and thermistors must be connected to a control. The control must be able to stop operation of the generator or creates some type of notification for the operator that a problem exists.

Thermistor - Resistive Temperature Device (RTD)

An RTD is a calibrated resistance element. RTD operation is based on the principle that the electrical resistance of a metallic conductor varies linearly with temperature changes. The terminals of the detector must be connected to a control panel which includes a temperature gauge.

Note: The RTD type thermistor allows monitoring of the absolute temperature. The information provided by the RTD is used to provide a temperature reading. The RTD is also used as an input for parameters that are set for alarm and shut down events according to preset temperatures.




Illustration 1g03775207

The following formula is used to convert the value of the resistance to a temperature measurement for a PT 100 thermistor.




Illustration 2g03776184

Ω = resistance measured on the PT-100

The protective devices, when requested, are shown in the wiring diagram specific to each generator.

Temperature Limits for the Windings

The temperature of the winding must be kept below the temperature limit rating of the thermal class of the insulation on the winding. The total temperature is determined by the following:




Illustration 3g03795231

Refer to Illustration 3 for the total temperature calculation.

Note: The ambient temperature is typically considered up to 40° C (104° F).

Above 40° C (104° F), the working conditions are considered special. Table 1 shows the numerical values and composition of the permitted temperature of the hottest point of the winding.

Table 1
Insulation Class     F     H    
Ambient temperature    
40° C (104° F)    

40° C (104° F)    
T = temperature rise (resistance method)    
105° C (221° F)    

125° C (257° F)    
Difference between the hottest point and the average temperature    
10° C (50° F)    

15° C (59° F)    
Total: Temperature of the hottest point    
155° C (311° F)    

180° C (356° F)    

Note: If the generator is exposed to winding temperatures above the values listed in Table 1, the service life of the insulation and service life of the generator is reduced substantially. A high operating temperature can cause the generator to melt insulation and short the windings causing a fire.

Thermal Protection for the Bearings

Temperature sensors are available for installation on the bearings. The sensors are to protect the bearings from damage due to overheating.

Alarm and Shut Down

The temperature parameters for unit alarm and shutdown must be set as low as possible. The temperatures can be determined based on the results of tests or by the operating temperature of the generator. The temperature for initiating an "Alarm" should be set as follows:

  • 10° C (50° F) above the operating temperature of the generator

  • While at full load

  • Consider the highest ambient temperature where the unit is installed

The temperature that will cause a shutdown must be set to a lower temperature than the temperatures listed in Table 2 and Table 3.

Table 2
Stator Winding (1)    
Class of Insulation     Maximum temperature of protection setting    
Alarm Shut down    
F    
140° C (284° F)    

155° C (311° F)    
H    
155° C (311° F)    

180° C (356° F)    
( 1 ) Maximum temperature of stator - continuous duty

Note: The temperature for generators that are used in emergency standby systems can be allowed up to 25° C (77° F) above the temperature for continuous operation. The allowance in temperature per the standard NEMA MG 1 and MG-22:40-1- 22.84. Generators that are installed in higher temperature conditions reduce the service life of the generator.

Table 3
BEARINGS    
Maximum Temperature Setting    
Alarm     Shut down    

110° C (230° F)    

120° C (248° F)    

Space Heater

Some generators are equipped with a heater to prevent condensation of water that can occur due to long periods without operation. The heater must be programmed to turn on after the shutdown of the generator and turn off before the unit is placed into operation. The required power for the space heater is shown on the identification plate that is located on the generator.

Note: If the space heater remains energized while the machine is in operation, generator windings may be damaged.

Auxiliary Winding Protection

The generator uses a fuse to protect the auxiliary winding and/or the voltage regulator against overload. The fuse is connected in series with the auxiliary winding and/or the voltage regulator.

Note: Failure to use the specified fuse may result in burning of the auxiliary coil and the stator winding.

If the fuse is blown, the fuse must be replaced with another fuse of equal rating for voltage and current. The appropriate fuse ensures that the generator is protected. The fuse protects the generator and voltage regulator in the following situations:

  • Loss of reference (sensing) of the voltage regulator

  • Short circuit of the auxiliary coil output wiring, short circuit of the auxiliary coil, or by incorrect wiring connections at the voltage regulator

  • Short circuit of the output terminals of the voltage regulator

  • Operation at low speed while the under frequency (U/F) or V/Hz protection is disabled. (Refer to the following note.)

  • Damage to the voltage regulator

Note: The customer can maintain a low speed (idle) for the generator set for an extended time for heating the engine, desired testing, or pre-lube. If the under frequency (U/F) or V/Hz protection is disabled, excessive excitation current in the main rotor can happen. The situation can result in a blown that protects the auxiliary winding and/or the voltage regulator.

Note: Damage of the voltage regulator can lead to overheating of the power element or loss of the internal reference signal. If the reference signal is lost, the circuitry will have nothing for comparison of signals.

Note: The fuse does not provide protection against a short circuit of the generator phases. The protection for a generator short circuit must include a relay that prevents the unit from starting.

Diode Protection

The diodes are protected against over voltage and/or power surge. Refer to Table 4. If the components fail, the components must be replaced.

Table 4
    Varistor     Capacitor    
C15 (GS919) and C18 (GS625) units     X     X    
Type of assembly     THT     THT    
Features     1W, 745 Vcc, 550 Vca, 210J/2ms     0.1µf, 2000 Vcc, 630 Vca    

Voltage Regulator Protection

Protection Against Under Frequency

The following must be done before placing the generator into operation:

  1. The under frequency protection of the voltage regulator must be set at 90% of the nominal frequency. The parameter is set at the factory.

  1. Leave the voltage regulator de-energized until the unit reaches the rated speed.

    Note: The precaution in Step 2 avoids over current problems in the auxiliary coil windings and excitation of the generator.




Illustration 4g03775783
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