Application Engineering

Please read the Warranty Statement carefully before proceeding with any design or ordering materials or labor.

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Planning the electrical design of the on-site power generation and distribution system is critical for proper system operation and reliability. This chapter covers installation design of the generator and related electrical systems; their interface with the facility and topics regarding load and generator protection.

The electrical installation of the generator set must follow local Electrical Code and should be accomplished by qualified electrical contractors who are experienced in power generation systems.

In view of the wide differences in applications, facilities and codes, specific details for on-site generator must be left to engineering judgment. This chapter gives general requirements for the electrical system design.

Requirements and Recommendations:

• The electrical design should ensure that the possibility of generator supply interruption is minimized. Physical separation of cables, controls and switchgear will help to ensure that a fault on one system will not compromise the other.
• Inclusion of bypass equipment will allow generator and utility switchgear to be maintained without risk.
• Generators move during start-up and shut-down. Check that the cable installation is able to accommodate movement. Stub-up arrangements must also allow for these movements.
• Cables and cable mounting systems must not be allowed to compromise vibration isolation.
• Control wiring should be run separately from power cabling to minimize interference.
• Circuit breakers and switchgear must be chosen to adequately break the fault current of the generator, together with any input from other generators or the utility supply.
• The tripping characteristics of a main-line circuit breaker must match the fault current produced by the alternator. If sizing a main-line circuit breaker, check the alternator decrement curve and the circuit breaker characteristic to ensure that tripping is possible under fault conditions.
• Use of Power Command controls with Amp Sentry may remove the need to include a main-line circuit breaker. Amp Sentry protects the alternator to the thermal damage characteristic and is graded to protect the connecting cables.
• Applications that require a single generator set, or a set of paralleled generators to energize unloaded transformer(s) as a part of their sequence of operation (such as an emergency power for a ring bus configuration) should be reviewed to verify the coordination of the protective functions. The review should also include the overcurrent protection to ensure that no nuisance tripping occurs when the transformer(s) is/are energized.
• Code and standards may require that an isolator is fitted if the main-line circuit breaker is omitted.
• Calculate the current carrying capacity and voltage drop of main power cables in accordance with the cable manufacturer’s rating charts and local codes and standards.
• Leading power factor loads may result in loss of voltage control. Ensure that the generator set is not exposed to greater than 10% of its rated kVAr capacity as leading kVAr. Avoid connecting bulk power factor correction equipment to the generator.
• The electrical system must be grounded in accordance with local electrical code. Cummins Power Generation products are designed to be operated in a ground-referenced system environment - consult your local distributor if considering un-grounded operation.
• Separately excited (e.g. Permanent Magnet Generator) alternators will produce up to 10 times full load current at the instance of fault, decaying to approximately 3 times full load current when controlled by Power Command Control AmpSentry.
• Self excited alternators will produce up to 10 times full load current at the instance of fault, which will rapidly decay to a value well below full load current within a few cycles.

For information regarding your application contact your nearest distributor.

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