GE N60 Instruction Manual page 63

CHAPTER 3: INSTALLATION
Table 3-4: Discharge period
Battery voltage (V) Input impedance (kΩ)
130 50
250 97
Debounce time setting = 2 ms
Assume a stray capacitance of 0.1 μF.
Assume an initial voltage across the stray capacitance "Vinitial" = 19 V (Vthreshold - 65 V).
Therefore, discharge time constant (τ) =50 kΩ *0.1 μF = 5 ms.
Discharge period t is calculated from the following equation:
Therefore, in this example the contact inputs operate.
To prevent this operation, the debounce time must be increased to 4 ms (set debounce time as per the following table) or
insert a resistor less than or equal to "R" as calculated later.
Table 3-5: Typical debounce time setting
Stray capacitance (μF) Battery voltage (V)
0.05 130
0.1 130
0.2 130
0.05 250
0.1 250
0.2 250
The value of this resistor "R" is calculated as follows:
1. Determine the minimum voltage (V threshold) required to turn on the input. This is determined by direct measurement
or referenced in the input specifications.
2. Calculate the resistance necessary to limit the voltage to 1/3 V threshold (when the contact is Open) as follows:
The 2 mA current is used in case the contact input is connected across the GE Form A contact output with voltage
monitoring. Otherwise use the amperage of the active circuit connected to the contact input when its contact output
is open and the voltage across the contact input is third trigger threshold to calculate the resistor value.
3. When the contact is closed, the battery voltage appears across the resistor. The wattage rating of the resistor is then:
4. Applying the following equation to our example:
5. Calculating the voltage across the contact input with the Burden Resistor, Voltage across the contact Input:
In conclusion, in this example, the contact input does NOT operate falsely with the Burden Resistor across its input AND
when a battery ground is present.
N60 NETWORK STABILITY AND SYNCHROPHASOR MEASUREMENT SYSTEM – INSTRUCTION MANUAL
Vthreshold = (Vbatt - VInitial) *e^ (-t/τ)
84 = -149 *e^ (t/0.005)
T = -0.005 * ln (84/149) = 0.0029 s
Debounce time (ms)
2
4
6
3
6
11
R = (Vthreshold / 3) / (2 mA*)
PR = 1.3 * (Vbatt) ^2 / R Watts
R = 84 V / 3*(1 / 2 mA) = 14 kΩ
PR = 1.57 Watts
Vresistor = 2 mA * 14 Kohm = 28 V
Vresistor < contact input threshold (84 V)
WIRING
3
Eq. 3-1
Eq. 3-2
Eq. 3-3
Eq. 3-4
Eq. 3-5
3-19