Arteche smART P500, Instruction Manual

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7BRELIABILITY INDEXES
PROTECTION, CONTROL AND METERING FUNCTIONS
To measure system performance, the electric utility industry has developed several
performance measures of reliability. These reliability indices include measures of outage
duration, frequency of outages, system availability, and response time.
System reliability is not the same as power quality. System reliability pertains to sustained
interruptions and momentary interruptions. Power quality involves voltage fluctuations,
abnormal waveforms, and harmonic distortions. An interruption of greater than five minutes
is generally considered a reliability issue, and interruptions of less than five minutes are a
power quality concern
The smART P500 relay has the ability to register the most important reliability indexes for
distribution networks as described below.
2.7.1. SYSTEM AVERAGE INTERRUPTION DURATION INDEX
The most often used performance measurement for a sustained interruption is the
System Average Interruption Duration Index (SAIDI). This index measures the total
duration of an interruption for the average customer during a given time period. SAIDI is
normally calculated on either monthly or yearly basis; however, it can also be calculated
daily, or for any other time period.
To calculate SAIDI, each interruption during the time period is multiplied by the duration
of the interruption to End the customer-minutes of interruption. The customer-minutes of
all interruptions are then summed to determine the total customer-minutes. To End the
SAIDI value, the customer-minutes are divided by the total customers (NTC). The
formula is,
( ) ( )
NTC
T C
SAIDI
i i
∑
=
It represents the average interruption time for the customers in the circuit.
2.7.2. CUSTOMER AVERAGE INTERRUPTION DURATION INDEX
Once an outage occurs the average time to restore service is found from the Customer
Average Interruption Duration Index (C AIDI). C AIDI is calculated similar to SAIDI