Neutral Grounding Resistor
Neutral Ground Rezistor Germany Europe
|
Neutral grounding resistor solutions are produced in Germany, Europe. The neutral ground resistor solution is our newest technological designed resistor for transformer centers to supply security to the transformer centers to manage the line security. Neutral Grounding Resistor is manufactured and designed to reduce technical problems like insulation breakdown caused by transient over-voltages produced by arcing ground faults in ungrounded systems and damage to prevent motors and switchgear caused by arcing in solidly grounded systems. The two main methods of system neutral grounding are low resistance and high resistance. The neutral grounding resistance system will trip to protect in the case of a line to ground fault. The neutral grounding resistor will limit the ground fault to a maximum of 100amper to 1000 Amper. The zero sequence neutral grounding resistors are for the transformers and ground fault relays will detect the fault and trip at 5 to 20% of the maximum ground fault current so can be monitored.
|
|
The neutral grounding resistor is generally rated for 10 seconds with a maximum temperature rise up to 800Celsious. The maximum ground fault current allowed by the resistor has to be large enough to positively actuate the applied ground fault relay. 200Amper to 400Amper rated neutral grounding resistors are fully used for the transformers from 6.9 kV till 34.5 kV systems .The 100Amper to 400 A rated neutral grounding resistors are generally used in 2.4 to 4.16 kV systems. Once the current and ohm rating is decided, the resistance or ohmic value of the resistor is calculated by dividing the line to neutral voltage by the Current Rating. For a 4.16 kV System neutral grounding resistor rated at 400 A. The line to neutral voltage will be 4.16 kV /√(3) = 2400 V. The needed neutral grounding resistance will be 2400 Volt / 400 Volt = 6 Ohms High Resistance.
The transformer system will alarm but not trip in the case of a Line to Ground fault. It is recommended for systems where power interruption resulting from single line to ground fault tripping is detrimental to the process. The neutral grounding resistor will limit the ground fault to a maximum of 5 Amper to 10 Amper . Zero sequence current transformers and ground fault relays will detect the fault and alarm at 5% to 25% of the maximum ground fault current occured at the transformer side. The neutral grounding resistor is rated for continuous duty with a maximum temperature rise of 400 Celsious. The maximum ground fault current allowed by the neutral grounding resistor must exceed the total capacitance to ground charging current of the system and the vector sum of the system charging current plus the resistor current shall not exceed 8 Amper. If you check the capacitance to ground charging current calculation. Once the current rating is determined, the resistance or ohmic value of the resistor is calculated by dividing the Line to Neutral Voltage by the Current Rating. For example for a 480 volt system neutral grounding resistor rated at 5 Amper. The line to neutral voltage will be 480 V /√(3) = 277 Volt. |
Neutral Ground Resistor Technical DatasheetBasic need as a required resistance will be 277 volt / 5amper = 55.4 Ohms. In medium voltage line power systems low resistance is generally used with a neutral grounding resistor that will limit the ground fault to a maximum of 25 amper to 50 amper. This is necessary to limit the touch voltage to 100 Volt or less volt. Zero sequence current transformers and ground fault relays detect the fault and will trip at less than one third of the resistor rating to secure the protection.
The neutral grounding resistor is rated for continuous duty with a maximum temperature rise of 375 celcious. Modern mine power systems can have a significant amount of distributed system capacitance and as will all neutral grounding resistors the maximum ground fault current allowed by the resistor must exceed the total capacitance to ground charging current of the system and the vector sum of the system charging current plus the resistor current shall not exceed 8 Amper. The references industrial power systems system neutral resistance grounding. |
|
|
|