Emergency Power Testing

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Key Questions

The following key questions are answered in this module:

What is a generator?
The generator is a rotary-motion, electro-mechanical device designed to create electricity when it is spun at the correct speed.

What is the most common internal combustion engine used to drive generators?
The most common internal combustion engines used to drive generators are diesel-fueled engines.

What is an automatic transfer switch (ATS)?
The automatic transfer switch (ATS) is a "smart" electro-mechanical device intended to automatically switch a load from the normal, utility-supplied power, over to generator-supplied power.

What is the Federal governing agency overseeing generators?
The National Fire Protection Association (NFPA) oversees generators.

What is load shedding?
Load shedding reduces the generator's electrical load in order to prolong its operating time.

Sample Video Transcript

Below is a transcript of the video sample provided for this module:

The automatic transfer switch is a “smart” electro-mechanical device intended to automatically switch a load from the normal, utility-supplied power, over to generator-supplied power. These switches monitor utility-supplied voltage, and when the voltage drops below a normal operating level for a pre-determined period of time (usually 20-30 seconds), the following sequence takes place: 1. The generator will start and its voltage allowed to stabilize (~5 seconds) 2. The ATS will disconnect the utility power from the load 3. The ATS will connect the generator power to the load The purpose of the initial 20-30 second delay is to assure that the utility dropout is not just a short-term “glitch” (power destabilization), but is a real power interruption. If so, the generator should start and take over the utility’s power-supply duties. When utility power has been restored and has remained stable for a period of time (this varies, but usually 10-15 minutes), depressing a button on the front of the ATS will disconnect the generator and re-connect the load to the now-stable utility power. Depending on the complexity of the system, this action may also automatically shut down the generator after an additional 5 or 10 minutes of running. The extra running time is typically added just-in-case the utility power wasn’t really as stable as was assumed, and generator power needs to be re-connected. There are some very sophisticated automatic transfer switches which require no human intervention at all. They will monitor whether the utility-supplied power has been restored, and has stabilized, and will automatically switch back from the generator to the utility supply. Then, if there is no instability in the utility power, they will turn the generator off. For most systems, this last example is the preferred type of switch, as it requires no human interaction at all, except routine inspections and testing.