GE Multilin C60 Breaker Protection System 3-213 HARDWARE 3.2 WIRING3APPLICATION EXAMPLEThis example is for illustrative purposes only and the calculations present the worst-case scenario. In practice, the value ofdebounce time can be lower.Contact input ON state impedance used in the calculation of the discharge period is based on the following table.Debounce time setting = 2 msAssume a stray capacitance of 0.1 μF.Assume an initial voltage across the stray capacitance "Vinitial" = 19 V (Vthreshold - 65 V), where Vthreshold = 84 V. Theinitial voltage Vinitial depends on values of impedance of R1 and contact inputs when the contact input is OFF (non-acti-vated state).Therefore, discharge time constant (τ) =50 kΩ *0.1 μF = 5 ms.Discharge period t is calculated from the following equation:Vthreshold = (Vbatt - VInitial) *e^ (-t/τ)84 = -149 *e^ (t/0.005) (EQ 3.1)T = -0.005 * ln (84/149) = 0.0029 sTherefore, 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) orinsert a resistor less than or equal to "R" as calculated later.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 measurementor referenced in the input specifications.2. Calculate the resistance necessary to limit the voltage to 1/3 V threshold (when the contact is OFF, the non-activatedstate) as follows:R = (Vthreshold / 3) / (2 mA) (EQ 3.2)The 2 mA current is used in case the contact input is connected across the GE Form A contact output with voltagemonitoring. Otherwise use the amperage of the active circuit connected to the contact input when its contact output isopen and the voltage across the contact input is third trigger threshold to calculate the resistor value.3. When the contact is ON (operate state), the battery voltage appears across the resistor. The wattage rating of theresistor is then:PR = 1.3 * (Vbatt) ^2 / R Watts (EQ 3.3)4. Applying the following equation to our example:R = 84 V / 3*(1 / 2 mA) = 14 kΩPR = 1.57 Watts (EQ 3.4)5. Calculating the voltage across the contact input with the Burden Resistor, Voltage across the contact Input:Table 3–3: DISCHARGE PERIODBATTERY VOLTAGE (V) INPUT IMPEDANCE (KΩ)130 50250 97Table 3–4: TYPICAL DEBOUNCE TIME SETTINGSTRAY CAPACITANCE (μF) BATTERY VOLTAGE (V) DEBOUNCE TIME (MS)0.05 130 20.1 130 40.2 130 60.05 250 30.1 250 60.2 250 11
