BE1-46N Functional Description
3-3
Heat Energy
0
,
T
(i
2
)
2
dt
Heat Energy
0
,
T
(i
2
)
2
dt < K
Heat Energy < (i
2
)
2
T
I
2
per unit
(i
2
)
Full Load Stator Current
Table 3-1. Wide Range Power Supply Voltage Ranges
Power Supply
Style Chart Identifier
Nominal Voltage
Voltage Range
Low Range
R
24 Vdc
12† to 32 Vdc
Mid Range
O, P, S
48, 125 Vdc,
120 Vac
24 to 150 Vdc,
90 to 132 Vac
High Range
T
125, 250 Vdc,
120, 240 Vac
62 to 280 Vdc,
90 to 270 Vac
† 14 Vdc required to start the power supply.
Relay operating power is developed by the wide range, isolated, low burden, flyback switching, solid-state
power supply. Nominal ±12 Vdc is delivered to the relay internal circuitry. Input (source voltage) for the
power supply is not polarity sensitive. A red LED turns ON to indicate that the power supply is functioning
properly.
POWER SUPPLY STATUS OUTPUT
The power supply status output relay has normally closed (NC) output contacts. This relay is energized
upon power-up thus opening its contacts. Normal relay operating voltage maintains the power supply status
output relay continually energized and its output contacts open. However, if the power supply output voltage
falls below the requirements for proper operation, the power supply status output relay de-energizes, thus
closing the NC output contacts.
SETTING CONSIDERATIONS
As the generator is subjected to unbalanced currents, the heating of the generator can be expressed in
terms of negative sequence current and time. The following mathematical relationship defines the
permissible heat energy tolerable to the generator without causing damage:
To avoid damage to the generator, the heat energy must be less than some value K as provided by the
generator manufacturer. The K value is a machine constant representing maximum permissible heating.
This value varies depending upon the generator design. K values normally range from 4 to 40. The
allowable heat energy is then expressed as:
Or, as: the instantaneous negative sequence current is equal to some constant I
2
which is expressed in per
unit of full load stator current. The formula is now expressed as:
For clarification, the following definitions are included.
K
= machine constant supplied by generator manufacturer representing the maximum
permissible thermal capacity of the generator rotor
T
= time in seconds
i
2
= instantaneous negative sequence current
I
2
pu
= negative phase sequence overcurrent expressed in per unit of full load stator current
Where:
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