Introduction
Dead tank and live tank circuit breakers are widely used in high-voltage applications. Circuit breakers play a crucial role in power system protection by interrupting fault currents and ensuring grid stability. While both serve the same fundamental purpose, they differ significantly in design, insulation, operation, and application.
Understanding these differences is essential for engineers, utility operators, and power system professionals to select the appropriate breaker for their specific needs. In this blog, we will explore the key distinctions between dead tank and live tank circuit breakers, their advantages, and the scenarios where each type is most suitable
Dead Tank Circuit Breaker
A dead tank circuit breaker is a high-voltage breaker whose switching or interruption occurs within a tank at ground potential. In other words, the tank in which the opening and closing of contacts occur is at ground potential. The incoming and outgoing conductors are taken at the insulated bushings, as shown in Figure 1.
Due to the design and construction of dead tank circuit breakers, current transformers are installed within the bushings to measure current for protection and metering applications. However, these CTs are relatively expensive compared to live tank circuit breakers of similar ratings.
The voltage range applications for a dead tank circuit breaker differ based on the manufacturer’s capability. For instance, GE offers dead tank circuit breaker that supports applications up to 550 kV and can carry continuous current up to 5000 A.
Live Tank Circuit Breaker
This type of circuit breaker causes interruption or switching (the opening/closing of contacts) in an insulator (bushing) that is at potential or voltage above ground.
Live tank breakers may seem simple in construction (in terms of structure or parts) but could have a higher voltage rating range compared with dead tank circuit breakers. They are also comparably cheaper and require less space.
If a project’s economics and space availability are constraints, then live tank circuit breakers are ideal. GE offers live tank breakers ranging from 72.5 kV to 800 kV. Some applications could go as far as 1,100 kV if needed. Figure 2 shows a live tank circuit breaker.
Factors to Consider when Selecting a High Voltage Circuit Breaker
Dielectric Medium
The opening and closing of circuit breaker contacts results in arcs during the interruption, which are even higher at high voltages. Therefore, it is important to quench this arc using a dielectric medium. There are many kinds of dielectric mediums, such as sulfur hexafluoride (SF6), vacuum, oil, air blast, etc.
Frequency
A frequency of 50 Hz or 60 Hz should be specified, depending on the region or country of use. In most parts of the world (about 80%), the grid operates at 50 Hz; in the United States, Canada, and some other countries, it uses 60 Hz. This is a list of countries with either 50Hz or 60Hz frequencies. Check where the breaker is going to be installed and select it appropriately.
Rated Voltage
Specify the line or system voltage under which the circuit breaker will be used. For instance, if the system voltage is 800 kV, then such voltage should be specified as the rated voltage of the circuit breaker.
Short Circuit Current
Equipment’s short circuit ratings are usually selected based on a short circuit study that indicates the maximum amount of fault (bolted fault current) contribution towards each device in a circuit. For high-voltage systems, this current will even be less. Manufacturers have specified short circuit currents at high or (any) voltages that could be selected during equipment ordering.
Minimum Temperature
Temperature is a key factor that affects the normal operating conditions of devices, and circuit breakers are no exception. Higher temperatures tend to derate the current carrying capacity of equipment due to added heat. Heat is usually energy lost and contributes to starting fires.
More importantly, cold weather tends to increase the amount of voltage an equipment will handle. Increasing voltages beyond the rated voltage will damage the equipment insulation, thereby leading to short circuit faults. The weather conditions of the location where the circuit breaker will be installed should be checked and considered during the selection of breakers.
Altitude
At higher altitudes, the amount of cooling air circulation decreases, and the dielectric strength of the quenching medium is also affected. Circuit breakers would derate in rated continuous current and voltage at altitudes greater than 6600 feet or 2000 m. Find altitude derating values and their correction factors by Schneider Electric.
Applications
Dead tank (DT) circuit breakers
Pros
- They come compact with embedded current transformers (CTs), reducing the cost of purchasing separate CTs.
- Can operate in extreme temperatures of -60 up to +60 ͦC.
- Can operate in high-polluting conditions and/or corrosive environments
- They have over 10,000 mechanical operations guaranteed, typically by manufacturers
- Less emission rate of about 0.5% per year
- More resilient to earthquakes or vibrations compared to live tank breakers
Cons
- Dead tank circuit breakers occupy more space due to their construction
- Uses more dielectric medium SF6 gas as an arc-quenching material
- SF6 is a greenhouse gas and still would contribute to global warming despite small quantities of release per annum.
- Expensive relative to the similar rating of a live tank breaker
- Less voltage range capability as shown in Figure 3.
Live tank (DT) circuit breakers
Based on the voltage and other specifications listed above, live tank breakers have several application ranges and advantages.
Pros
- They are easy to install due to fewer parts or components to assemble
- A long period of service before inspections are due. Siemens has periods of up to 25 years
- Enormous switching operations are guaranteed up to 10,000
- They have a long life span of up to 50 years in operations.
- Occupies less space
- Less amount of dielectric medium (SF6) filled in the interruption chamber relative to the dead tank breaker.
- An emission rate of less than 0.1% per annum
- Wide temperature range (extreme cold to high, -60 up to +60 ͦC) applications depending on manufacturer’s product capabilities.
- Wide voltage range capability as shown in Figure 4.
Cons
- SF6 is a greenhouse gas and still would contribute to global warming despite small quantities of release per annum.
- Separate current transformers are typically needed for measurement applications
- Less resilient towards natural events such as earthquakes.
Video Credit: Gaurav J – TheElectricalGuy
Top 10 Manufacturers of Circuit Breakers
- General Electric, GE
- ABB Limited
- Siemens AG
- Alstom
- Eaton Corporation
- Schneider Electric, SE
- Mitsubishi Electric Power Products, Inc
- G & W Electric Co
- Camsco Electric Co. Ltd
- Toshiba Corporation
Others include:
- Kirloskar Electric Co. Ltd
- Powell Industries Inc
- Schurter Holding AG
- Larsen & Toubro Limited
- Sensata Technologies Inc
Summary
Dead tank and live tank circuit breakers are essential components in power system protection but differ in design, operation, and applications. A dead tank circuit breaker’s interrupting chamber is housed in a grounded metal enclosure, making it safer, more stable, and suitable for high-voltage substations. In contrast, a live tank circuit breaker’s interrupting chamber is insulated and elevated, reducing insulation costs and making it ideal for outdoor installations and compact substations.
- Insulation & Safety: Dead tanks offer better grounding and reliability, while live tanks require higher insulation but are cost-effective.
- Size & Maintenance: Dead tanks are larger but easier to maintain; live tanks are more compact but require careful handling.
- Application Suitability: Dead tanks are preferred for higher voltage levels, while live tanks are commonly used for medium to high voltages (refer to Figures 3 and 4). Check with the manufacturer for design capabilities. For instance, refer to the Siemens module design for HV dead and live tank circuit breakers for project-specific needs.
The decision to choose between them depends on factors like voltage rating, installation space, and maintenance needs. Understanding these differences is crucial for selecting the right breaker for a safe and efficient power system.
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