Protection of Electrical Networks

Christophe Prévé

• Publisher: Wiley-ISTE
• Year: 2013
• Print ISBN: 9781905209064
• eBook ISBN: 9781118614129
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

This book, designed for engineers, technicians, designers and operators working with electrical networks, contains theoretical and practical information on the design and set-up of protection systems.
Protection of Electrical Networks first discusses network structures and grounding systems together with problems that can occur in networks. It goes on to cover current and voltage transformers, protection functions, circuit breakers and fuses.
Practical explanations of how protection systems function are given, and these, together with tables of settings, make this book suitable for any reader, irrespective of their initial level of knowledge.

Chapter 1

Network Structures

Definition

Standard IEC 60038 defines voltage ratings as follows:

– Low voltage (LV): for a phase-to-phase voltage of between 100 V and 1,000 V, the standard ratings are: 400 V - 690 V - 1,000 V (at 50 Hz).

– Medium voltage (MV): for a phase-to-phase voltage between 1,000 V and 35 kV, the standard ratings are: 3.3 kV - 6.6 kV - 11 kV - 22 kV - 33 kV.

– High voltage (HV): for a phase-to-phase voltage between 35 kV and 230 kV, the standard ratings are: 45 kV - 66 kV - 110 kV - 132 kV - 150 kV - 220 kV.

In this chapter we will look at:

– types of HV and MV consumer substations;

– structure of MV networks inside a site;

– structure of LV networks inside a site;

– structure of systems with a back-up power supply.

Six standard examples of industrial network structures are given at the end of the chapter.

Each structure is commented upon and divided up so that each functional aspect can be considered.

(NC) means that the switch or circuit-breaker is closed in normal conditions.

(NO) means that the switch or circuit-breaker is open in normal conditions.

Figure 1-1: structure of a private distribution network

1.1. General structure of the private distribution network

Generally, with an HV power supply, a private distribution network comprises (see Figure 1-1):

– an HV consumer substation fed by one or more sources and made up of one or more busbars and circuit-breakers;

– an internal generation source;

– one or more HV/MV transformers;

– a main MV switchboard made up of one or more busbars;

– an internal MV network feeding secondary switchboards or MV/LV substations;

– MV loads;

– MV/LV transformers;

– low voltage switchboards and networks;

– low voltage loads.

1.2. The supply source

The power supply of industrial networks can be LV, MV or HV. The voltage rating of the supply source depends on the consumer supply power. The greater the power required, the higher the voltage must be.

1.3. HV consumer substations

The most usual supply arrangements adopted in HV consumer substations are:

Single power supply (see Figure 1-2)

Advantage:

– reduced cost.

Disadvantage:

– low reliability.

Note: the isolators associated with the HV circuit-breakers have not been shown.

Figure 1-2: single fed HV consumer substation

Dual power supply (see Figure 1-3)

Figure 1-3: dual fed HV consumer substation

Operating mode:

– normal:

- Both incoming circuit-breakers are closed, as well as the coupler isolator.

- The transformers are thus simultaneously fed by two sources.

– disturbed:

- If one source is lost, the other provides the total power supply.

Advantages:

– Very reliable in that each source has a total network capacity.

– Maintenance of the busbar possible while it is still partially operating.

Disadvantages:

– More costly solution.

– Only allows partial operation of the busbar if maintenance is being carried out on it.

Note: the isolators associated with the HV circuit-breakers have not been shown.

Dual fed double bus system (see Figure 1-4)

Operating mode:

– normal:

- Source 1 feeds busbar BB1 and feeders Out1 and Out2.

- Source 2 feeds busbar BB2 and feeders Out3 and Out4.

- The bus coupler circuit-breaker can be kept closed or open.

– disturbed:

- If one source is lost, the other provides the total power supply.

- If a fault occurs on a busbar (or maintenance is carried out on it), the bus coupler circuit-breaker is tripped and the other busbar feeds all the outgoing lines.

Advantages:

– Reliable power supply.

– Highly flexible use for the attribution of sources and loads and for busbar maintenance.

– Busbar transfer possible without interruption.

Disadvantage:

– More costly in relation to the single busbar system.

Note: the isolators associated with the HV circuit-breakers have not been shown.

Figure 1-4: dual fed double bus HV consumer substation

1.4. MV power supply

We shall first look at the different MV service connections and then at the MV consumer substation.

1.4.1. Different MV service connections

Depending on the type of MV network, the following supply arrangements are commonly adopted.

Single line service (see Figure 1-5)

The substation is fed by a single circuit tee-...

Table of contents

• Cover
• Title Page
• Copyright
• Chapter 1: Network Structures
• Chapter 2: Earthing Systems
• Chapter 3: Main Faults Occurring in Networks and Machines
• Chapter 4: Short-circuits
• Chapter 5: Consequences of Short-circuits
• Chapter 6: Instrument Transformers
• Chapter 7: Protection Functions and their Applications
• Chapter 8: Overcurrent Switching Devices
• Chapter 9: Different Selectivity Systems .
• Chapter 10: Protection of Network Elements
• Appendix A: Transient Current Calculation of Short-circuit Fed by Utility Network
• Appendix B: Calculation of Inrush Current During Capacitor Bank Energization
• Appendix C: Voltage Peak Value and Current r.m.s Value, at the Secondary of a Saturated Current Transformer
• Index