Live Tank Circuit Breakers Application Guide Edited by ABB AB High Voltage Products Department: Marketing & Sales Text: Tomas Roininen, Carl Ejnar Sölver, Helge Nordli, Anne Bosma, Per Jonsson, Anders Alfredsson Layout, 3D and images: Mats Findell, Karl-Ivan Gustavsson SE-771 80 LUDVIKA, Sweden 2 Application Guide | ABB Circuit Breakers Table of contents 1. Introduction 8 1.1 What is a circuit breaker? 8 1.2 Why do we need circuit breakers? 9 1.3 Different types of switching 9 1.4 Disconnecting and withdrawable circuit breakers 9 1.5 Circuit switcher 11 1.6 Environmental aspects 11 2. Live tank circuit breaker designs and operating principles 12 2.1 Historical development 12 2.2 Main components 13 2.2.1 Breaking unit 14 2.2.2 Support insulator 14 2.2.3 Operating mechanism 14 2.2.4 Support structure 14 2.3 Additional components 15 2.3.1 Grading capacitors 15 2.3.2 Preinsertion resistors 15 2.3.3 Cabinets for central control 15 2.4 SF6 Interrupters 16 2.4.1 SF6 gas 16 2.4.2 Principles of arc extinction 16 2.4.2.1 Thermal regime 17 2.4.2.2 Dielectric regime 18 2.4.3 Earlier interrupter designs 19 2.4.4 SF6 puffer circuit breakers 19 2.4.5 SF6 self-blast circuit breakers 22 2.4.6 Configuration of the moving contacts 25 2.5 Operating mechanisms 26 2.5.1 General 26 2.5.2 Spring-operated mechanism 27 2.5.3 Motor Drive 30 2.5.4 Pneumatic-operated mechanism 31 2.5.5 Hydraulic-operated mechanism 31 2.5.6 Hydraulic spring-operated mechanism 31 2.5.7 Other types of operating mechanisms 32 3. Current switching and network stresses 33 3.1 Short-circuit currents 33 3.1.1 Standardized time constant and asymmetry 35 3.1.2 Peak withstand current 36 3.2 Terminal faults 37 3.2.1 Transient Recovery Voltage (TRV) in single-phase networks 37 3.2.2 TRV in three-phase networks 40 3.3 Short-line faults 43 3.4 Initial Transient Recovery Voltage (ITRV) 45 3.5 Out-of-phase conditions 46 3.6 Switching of capacitive currents 47 3.6.1 De-energizing of capacitive loads 47 ABB Circuit Breakers | Application Guide 3 Table of contents 3.6.2 Recovery voltage 50 3.6.3 Energizing of capacitor banks 51 3.7 Inductive load switching 53 3.7.1 Switching of shunt reactors 53 3.7.1.1 Current chopping and resulting overvoltages 54 3.7.1.2 Reignitions 57 3.7.1.3 Overvoltages and overvoltage limitation 58 3.7.2 Switching of no-load transformers 59 4. Mechanical stresses and environmental effects 60 4.1 Mechanical loads 60 4.1.1 Static loads 60 4.1.1.1 Dead weight 60 4.1.1.2 Static terminal load 60 4.1.1.3 Ice load 62 4.1.1.4 Wind load 62 4.1.2 Dynamic loads 63 4.1.2.1 Dynamic loads due to operation 63 4.1.2.2 Dynamic current loads 64 4.1.3 Seismic load 65 4.1.3.1 Measures to increase seismic withstand levels 67 4.2 Combination of loads 67 4.3 Influence of extreme ambient temperatures 68 4.4 Gas properties 69 4.4.1 Effect of ambient temperature 69 4.4.2 Moisture content in SF6 gas 70 4.5 Sound effects of circuit breaker operation 71 4.5.1 Standards 71 4.5.2 Sound level as function of distance 71 5. Thermal stresses 72 5.1 Thermal limits 72 5.1.1 Derating of rated current due to temperature 72 5.2 Temperature rise test 73 5.3 Temperature rise at current overload 74 5.4 Influence of site altitude 76 6. Insulation requirements 78 6.1 Insulation co-ordination 78 6.2 Overvoltages 78 6.2.1 Short-duration power frequency voltage 78 6.2.2 Lightning impulse 78 6.2.3 Chopped impulse 80 6.2.4 Switching impulse 80 6.3 Insulation levels 81 6.4 Dielectric tests on circuit breakers 84 6.4.1 General 84 6.4.2 Combined voltage test 84 6.4.3 Other voltage tests 85 4 Application Guide | ABB Circuit Breakers 6.4.3.1 RIV (Radio Interference Voltage) tests 86 6.4.3.2 Partial discharge test 86 6.4.3.3 Pollution test 86 6.4.3.4 Tests on low-voltage circuits 86 6.5 Atmospheric correction factor 87 6.6 Installation at high altitudes 88 6.7 Environmental effects and insulator shapes 89 6.7.1 Creepage distance and pollution 89 6.7.2 Environmental classes according to IEC 90 6.7.3 Environmental classes according to IEEE 91 6.8 Clearances in air 92 6.9 Insulating material 93 7. Application 94 7.1 Transmission line circuit breakers 94 7.1.1 Faults on overhead lines 94 7.1.2 Switching of no-load transmission lines 95 7.1.2.1 Voltage factor 95 7.1.2.2 Line charging current 95 7.1.2.3 Reclosing 96 7.1.2.4 Shunt compensated transmission lines 96 7.1.2.5 Series compensated transmission lines 96 7.1.3 Classification 96 7.2 Power transformer circuit breakers 97 7.2.1 Asymmetry and d.c. time constant 98 7.2.2 No-load switching conditions 98 7.2.3 Synchronization 99 7.2.4 Classification 99 7.3 Capacitor/filter circuit breakers 99 7.3.1 Recovery voltage and voltage factors 100 7.3.2 Inrush current 100 7.3.3 Rating and classification 101 7.4 Shunt reactor circuit breakers 101 7.4.1 Operating conditions 102 7.4.2 Reignitions 103 7.4.3 Elimination of reignitions 103 7.4.4 Shunt reactor switching tests 103 7.4.5 Classification 104 7.5 Bus couplers 104 7.6 Special applications 104 7.6.1 Railway applications 105 7.6.1.1 Railway applications with a power frequency less than 50 Hz 105 7.6.2 Series capacitor by-pass switches 105 7.6.3 HVDC filters 106 7.6.4 SVC (Static Var Compensator) 107 7.7 Instrument transformers and relays in combination 107 with live tank circuit breakers 7.8 Controlled switching 108 ABB Circuit Breakers | Application Guide 5 Table of contents 8. Standards and tests 109 8.1 Standards 109 8.1.1 IEC 109 8.1.1.1 Time definitions according to IEC 110 8.1.2 ANSI/IEEE 111 8.2 Circuit breaker testing 111 8.3 Type tests 112 8.3.1 Dielectric tests 112 8.3.2 Radio Interference Voltage (RIV) tests 113 8.3.3 Temperature rise tests 113 8.3.4 Measurement of the resistance of the main circuit 113 8.3.5 Short-time withstand current and peak withstand current tests 113 8.3.6. Mechanical and environmental tests 114 8.3.6.1 Mechanical operation test at ambient temperature 114 8.3.6.2 Low and high temperatures tests/tightness tests 115 8.3.6.3 High temperature test 116 8.3.6.4 Humidity tests 117 8.3.6.5 Ice tests 117 8.3.6.6 Static terminal load test 117 8.3.7 Making and breaking tests 118 8.3.7.1 Preparation for tests 118 8.3.7.2 Single-phase/three-phase testing 118 8.3.7.3 Unit test/full pole test 119 8.3.7.4 Direct tests 119 8.3.7.5 Synthetic testing 120 8.3.7.6 Summary of test duties 121 8.3.7.7 Terminal fault 121 8.3.7.8 Short-line fault 121 8.3.7.9 Out-of-phase making and breaking tests 122 8.3.7.10 Capacitive current switching 122 8.3.7.11 Shunt reactor current switching tests 123 8.4 Routine tests 123 8.5 Test reports 123 8.5.1 Type test reports 124 8.5.2 Type test reports of independent laboratories 124 8.5.3 STL organization 124 8.5.4 SATS organization 125 9. Reliability, maintenance and life cycle costs 126 9.1 Failure statistics 126 9.2 Electrical and mechanical life 126 9.3 Maintenance 128 9.4 Condition monitoring 128 9.5 Life cycle costs 129 9.6 Environmental aspects 129 10. Selection of circuit breakers 131 6 Application Guide | ABB Circuit Breakers Scope This document gives background information for selection of the best possible circuit breaker solution for each particular application. The guide addresses utility, consultant and project engineers who specify and apply high-voltage circuit breakers. The guide addresses live tank circuit breakers in general for voltages up to 800 kV. The most usual requirements on a circuit breaker are mentioned, such as the capabilities to handle network stresses, insulation levels, mechanical forces and ambient conditions. The construction of circuit breaker poles and operating mechanisms will be mentioned only briefly since these parts are described in ABB Buyer’s Guide for Live Tank Circuit Breakers. ABB Circuit Breakers | Application Guide 7 1. Introduction 1.1 What is a circuit breaker? A circuit breaker is an apparatus in electrical systems that has the capability to, in the shortest possible time, switch from being an ideal conductor to an ideal insula- tor and vice versa. Furthermore, the circuit breaker should be able to fulfill the following requirements: 1. In the stationary closed position, conduct its rated current without producing impermissible heat rise in any of its components. 2. In its stationary positions, open as well as closed, the circuit breaker must be able to withstand any type of overvoltages within its rating. 3. The circuit breaker shall, at its rated voltage, be able to make and break any pos- sible current within its rating, without becoming unsuitable for further operation. The requirements on live tank circuit breakers may be as high as 80 kA current interrupting capability and 800 kV rated voltage. In addition to live tank circuit breakers, there are also other constructions of the circuit breaker poles (dead tank, GIS). In earlier times, oil and compressed air were typical insulating and extinguishing me- dium. Nowadays they are almost entirely replaced by SF6 gas for economical and practical reasons, and also due to increased demands for higher ratings. There are different types of operating mechanisms, e.g. spring-, hydraulic- and pneumatic-operated mechanisms, and recently digitally-controlled motors have come into use. Figure 1.1 Circuit breaker for 145 kV Figure 1.2 Circuit breaker for 420 kV 8 Application Guide | ABB Circuit Breakers 1.2 Why do we need circuit breakers? The circuit breaker is a crucial component in the substation, where it is used for coupling of busbars, transformers, transmission lines, etc. The most important task of a circuit breaker is to interrupt fault currents and thus protect electric and electronic equipment. The interruption and the subsequent reconnection should be carried out in such a way that normal operation of the network is quickly restored, in order to maintain system stability. In addition to the protective function, the circuit breakers are also applied for intentional switching such as energizing and de-energizing of shunt reactors and capacitor banks. For maintenance or repair of electrical equipment and transmission lines, the circuit breakers, together with the disconnectors, earthing switches or disconnecting cir- cuit breakers with built-in disconnecting function, will ensure personnel safety. 1.3 Different types of switching The requirement to switch any current within the circuit breaker’s rating includes dif- ferent making and breaking conditions: − Terminal faults, short-circuits in the vicinity of or near the circuit breaker. − Short-line faults, short-circuits to ground along the transmission line within a few kilometers of the circuit breaker. − Out-of-phase conditions at which different parts of the network are out of synchronism. − Intentional switching of capacitor banks, shunt reactor banks, no-load transformers, no-load lines and cables. In this connection controlled switching ought to be mentioned. This is described in ABB Controlled Switching, Buyer’s and Application Guide. The different switching conditions will be explained in Section 3, Current switching and network stresses. 1.4 Disconnecting and withdrawable circuit breakers It has been mentioned that the circuit breaker is an important element in the sys- tem, either as a ”stand-alone circuit breaker” in a conventional substation or as an integrated part of a compact switchgear assembly. The modern solutions with Disconnecting Circuit Breakers (DCB) and Withdraw- able Circuit Breakers (WCB) make it possible to develop new types of switchgear constructions. The purpose of the compact switchgear assembly is to simplify the switchgear and at the same time to improve the reliability of the system. ABB Circuit Breakers | Application Guide 9 1. Introduction The different types of compact switchgears have one thing in common elimination of the conventional disconnectors in the system. Disconnectors have basically the same failure rate as circuit breakers, but need more frequent maintenance. The DCB is a circuit breaker that satisfies the requirements for a circuit breaker as well as a disconnector. This is described in IEC 62271-108. Ratings for current and voltage are the same as for a circuit breaker, while the insulating levels comply with those for disconnectors. Disconnecting circuit break- ers are normally combined with remotely-operated earthing switches and inter- locking systems to provide increased safety. A DCB for rated voltage 145 kV is shown in Figure 1.3. In the WCB, the circuit breaker poles are mounted on a movable trolley and provided with additional contacts for the disconnector function. The movement of the trolley replaces the close/open function of the conventional disconnectors. See Figure 1.4. A WCB can be extended with a complete gantry and busbars. It is even possible to equip the WCB with current transformers or earthing switches. Availability studies have shown that in substations with DCB or WCB, the availabil- ity is considerably improved over that of conventional solutions. In addition to the low failure rate and long periods between maintenance, another advantage is the substantial reduction in space. Figure 1.3 Figure 1.4 Disconnecting Circuit Breaker (DCB) for 145 kV. Withdrawable Circuit Breaker (WCB) The earthing switch is painted in red and yellow. for 145 kV with busbars and gantry. 10 Application Guide | ABB Circuit Breakers