Types of radial systems

Question 1

• A single primary service and distribution
  transformer supplies all feeders.
• There is no duplication of equipment
• System investment is
  the lowest of all circuit arrangements
• Loss of a cable, primary supply, or transformer will cut off service.
• Equipment must be shut down to perform routine maintenance and servicing
• This system is satisfactory for small industrial installations where process allows sufficient
  down time for adequate maintenance, and the plant can be supplied by a single transformer.

Answer 1

Simple Radial System

Question 2

• may be applied to larger loads by using a radial primary distribution system to supply a number of unit substations located near the centers.
• The advantages and disadvantages are
  the same as those described for the simple radial system

Answer 2

Expanded Radial System

Question 3

• Each unit substation is connected to two separate primary feeders through switching equipment to provide a normal and an alternate source
• Cost is somewhat higher than for a radial system because of duplication of primary cable and switchgear
• but there will be an interruption until load is transferred to the alternate
  source.

Answer 3

Primary Selective System

Question 4

-The failure of the normal source of a primary cable fault can be isolated and service restored
by sectionalizing
-The system
may be dangerous because the quickest way to find a fault is to sectionalize the loop and
reclose.

Answer 4

Primary Loop System

Question 5

If pairs of unit substations are connected through a normally open secondary tie circuit
breaker, the result is a secondary selective system. If the primary feeder or a transformer
fails, the main secondary circuit breaker on the affected transformer is opened and the tie
circuit breaker closed.

Answer 5

Secondary Selective System

Question 6

In this system, two or more distribution transformers are each supplied from a separate primary distribution feeder.

Answer 6

Secondary Spot Network

Question 7

This is the most generally applicable and widely used form of industrial secondary network system. Each transformer in the primary selective network system is equipped with a
primary selector switch.

Answer 7

Primary Selective Secondary Network System