Impulses FAQ


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"ISO 9001:2000 Certified"

Impulses FAQ

Voltage sags, swells, or transient impulses can cause light flicker, interrupt sensitive electronic processes, or even cause permanent damage to electrical equipment. Standards for the disturbances discussed have not been established by any recognized utility standards creating group. Many guidelines have been created but the fact remains that each piece of equipment has a susceptibility profile and may or may not be affected by disturbances of specific magnitude and duration. With respect to voltage sags caused by motor starts, the department has found that the majority of complaints are resolved by the following criteria for 5-50hp motor starts:

Voltage fluctuations (including both transformer and service cables)

1. Air conditioning and other motors that do not start frequently

a. 4% deviation from steady state is allowed where other customers are affected

b. 6% deviation from steady state is allowed when the customer causing the problem is affected

2. Motor that have frequent starts, such as elevator motors a. 3% deviation from steady state is allowed where other customers are affected

These design and operating criteria are developed with respect to the service entrance. Larger voltage deviations within the customers premises due to internal wiring shall be the responsibility of the customer.

Presently for motors exceeding 50hp, the customer must get approval from Distribution Planning. Planning guidelines state that for this situation frequent starts shall limit voltage sags on our distribution system to 1% and infrequent starts to 2%. Any drops on the customers premises must be addressed by the customer although power quality will help evaluate compliance and offer recommendations. The percentages are conservative, but the Department has considered that complaints received for approval of larger percentages may not be easily or cost effectively solved.

With respect to disturbances not created by normal motor starts, the Department is committed to help customers in the resolution of these disturbances. Help will be provided through our experience gained in resolving other power quality problems, pertinent trade and industry paper and publication recommendations, recommended power quality consultant specialist reference list, and prudent cost effective, efficient, and reliable utility design where applicable.

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