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What parallel redundancy does to the power distribution system? What parallel redundancy does to the power distribution system? (photo credit: hipowersystems.com) Increasing reliability // Redundancy is a useful method of increasing reliability and optimising the balance between operation effectiveness and expenditure. In the context of reliability, redundancy signifies that a system will continue to function satisfactorily in spite of the failure of some of the component parts. This resilience to failures is obtained by providing alternative paths of operation, by arranging selected elements of the system in parallel. Generally, alternative paths of operation can be achieved by following: Standby Redundancy Active or Parallel Redundancy N+1 and 1+1 Redundancy
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What Parallel Redundancy Does to the Power Distribution System_ _ EEP

Jul 16, 2016

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Page 1: What Parallel Redundancy Does to the Power Distribution System_ _ EEP

What parallel redundancy does to the power distributionsystem?

What parallel  redundancy does  to  the power distribution system? (photo credit: hipowersystems.com)

Increasing reliability //Redundancy is a useful method of increasing reliability and optimising the balance betweenoperation effectiveness and expenditure. In the context of reliability, redundancy signifies that asystem will continue to function satisfactorily in spite of the failure of some of the componentparts.

This resilience to failures is obtained by providing alternative paths of operation, by arrangingselected elements of the system in parallel. Generally, alternative paths of operation can beachieved by following:

Standby RedundancyActive or Parallel RedundancyN+1 and 1+1 Redundancy

Page 2: What Parallel Redundancy Does to the Power Distribution System_ _ EEP

Standby Redundancy

Standby redundancy means that an alternative means of performing the function is provided butis inoperative until needed. It is switched on upon failure of the primary means of performing thefunction.

An example of standby redundancy would be the use ofa standby generator in a building to ensure continuity ofsupply in case of a mains failure. The generator is not calledfor until it is needed when the power supply fails.

Such a scheme would not be suitable for a computersystem, because data would be lost during the relativelylong period required to start the standby generator.

Backup standby generators  (photo credit: dchuddle.com)

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Active or Parallel Redundancy

In active or parallel redundancy, all redundant units are operating simultaneously rather thanbeing switched on when needed. The most obvious approach is to use two components, each

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capable of carrying the full load, so that if one should fail the other will take over – this is referredto as 1+1 redundancy.

An alternative approach is to split the load among a number of units, each capableof carrying only a fraction of the load, and provide just one additional redundant unit –this is referred to as N+1 redundancy. For very critical loads, more than one fully ratedredundant unit may be provided.

For example, a 1+2 redundancy scheme would have two fully rated redundant units supportingthe single operating unit and would require all three units to fail before the system fails. Becausethere is no interruption, active redundancy is suitable for computer installations.

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N+1 and 1+1 Redundancy

The theory of redundancy is that should a component within a system fail, the system willcontinue to function because alternative paths are available for the system to operate.

In Figure 1 the system will function with either A1 or A2 operating. Should component A1 fail, thesystem will continue to function.This type of redundancy is termed 1+1, as there is 100%redundancy available.

Figure 1 – 1+1 Redundancy

In the system shown in Figure 2 two out of the three components are required for the systemto function and there is one redundant component. In this scenario, the system would becalled 2+1. In each case, the first number refers to the number of components required for thesystem to function correctly and the second number refers to the number of standbycomponents available.

Figure 2 – N+1 Redundancy

It is possible to have many redundant components that would significantly improve the reliability ofthe system. However, this would also be expensive and in most applications a balance isachieved between reliability and economics.

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Figure 3 – Examples of  redundancy of power distribution system

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Load testing a 500kVA generator (VIDEO)

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Reference // A Good Practice Guide to Electrical Design – Copper Development Association