Mike Dolt Enterprises
Mike Dolt Enterprises
User: jimbo123, Location: Tucson, Az.
Asked on: Monday, April 4, 2011 at 5:32 am EDT
Answered on: Tuesday, May 14, 2024 at 3:43 am EDT
Question: This is a question on switchgear that is controlled by a plc when there is a power failure and the bu generator is supplying power to the switchgear. If one CB in the switchgear is in the off position and left in place so the only thing to put the CB back in service would be to close the CB.Our engineer said if the generator were to start up and supply power to the switchgear that it would try to close the opened CB. This to me doesn't sound right for that to happen, I have limited knowledge on SG and the plc start up.Does anyone know either way about this operation ?
The behavior of a circuit breaker (CB) in a switchgear controlled by a programmable logic controller (PLC) during a power failure and subsequent generator operation depends on the specific design and configuration of the system.
Typical Operation
In most cases, when a power failure occurs, the PLC will initiate a "black start" procedure. This procedure typically includes the following steps:1. Start the backup generator.
2. Transfer the switchgear to generator power.3. Close any open CBs that are necessary to restore power to critical loads.
CB in "Off" Position
If a CB is left in the "Off" position during a power failure, it is generally not expected to close automatically when the generator starts up and supplies power to the switchgear. This is because the PLC's black start procedure usually only closes CBs that are necessary to restore power to critical loads. An open CB that is not essential for power restoration would typically remain open.However, there could be some exceptions to this behavior, depending on the specific system design:
Configuration Error
If the PLC's configuration is incorrect, it may attempt to close all CBs, regardless of their state. This is a rare occurrence but could potentially happen.
Fault Condition
If the CB was opened due to a fault condition, the PLC may interpret this as a need to close the CB to isolate the fault. In this case, the CB could close automatically when the generator supplies power.
Recommendations:
To ensure proper operation of the switchgear, it is recommended to: Verify the PLC's black start procedure to confirm the expected behavior of CBs. Test the system during a simulated power failure to observe the actual behavior of the CBs.* Train operators on the proper procedures for closing CBs after a power failure.In summary, it is unlikely that a CB in the "Off" position would close automatically when the generator supplies power to the switchgear. However, it is important to verify the system's specific configuration and operating procedures to ensure proper operation. Flag for review