Distribution System Training

8038 — Abnormal Operating Conditions

Duration: 2.0 Hour(s)

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Power Distribution


The objective of this module is to draw attention to abnormal operating conditions that may arise on the distribution system. The operator is expected to recognize these conditions and take corrective action to enable the system to continue in operation.

After completion of this module and associated workbook, the participant should be able to understand the following concepts and apply them in day-to-day work activities.

  • Specific operating conditions which are considered to be abnormal
  • Established voltage tolerance at customers’ service entrances
  • Voltage control equipment
  • Causes of low voltage
  • The effect of increased voltage drop with increase in customer demand over time
  • Available changes in equipment installation to accommodate increase in load demand
  • Causes of high voltage, and corrective actions available to the operator
  • The capability of certain equipment to operate under overload conditions (say 50%)
  • The effect of overloading on equipment life expectancy
  • Transformer loading guide
  • The effect of pre-load magnitude and ambient temperature on overload consequences
  • The need to maintain updated records on the status of each substation transformer
  • The need for operating guidelines specifying acceptable transformer overload practices
  • Overloading step voltage regulators
  • Equipment that cannot tolerate overload above continuous rated capacity, i.e. switchgear, cables, overhead conductors
  • Operating conditions which result in the need to reduce customers’ load demand (load shedding)
  • System control of generation/load demand balance
  • The effect and consequences of falling frequency
  • Controlled voltage reduction by adjustment of distribution substation transformer on-load tap changers
  • The effect on load demand of voltage reduction
  • Disconnecting “interruptible” customer loads
  • Disconnecting primary feeders on a rotating basis, i.e. rolling black-outs
  • Exclusions from load shedding schedules, i.e. critical feeders and secondary distribution networks
  • Automatic load shedding by low frequency relays
  • The need for load shedding as a result of loss of transmission or sub-transmission capacity
  • The objectives of “load management” as distinct from load shedding
  • Manipulating the customer’s load to reduce peaks and fill in the valleys on the daily load curve
  • Customer incentives to facilitate load management
  • Automatic timer switching of selected loads
  • Remote switching of selected loads by the distribution operator
  • Automatic remote switching


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