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How To Choose A Suitable Circuit Breaker For Diesel Generator Set

Sep. 06, 2021

Several different criteria need to be considered when selecting a circuit breaker, including voltage, frequency, breaking capacity, continuous current rating, abnormal operating conditions, and product testing. Today, Jiangsu Starlight Electricity Equipments Co.,Ltd. will give you a step-by-step overview of how to select the appropriate circuit breaker for your specific application.

 

1. Rated voltage

The total rated voltage of circuit breakers available in different sizes and configurations is calculated based on the highest voltage that can be applied to all terminal ports, the type of power distribution, and how the circuit breaker is directly integrated into the system. It is very important to select a circuit breaker with sufficient voltage capacity to meet the final application.

 

2. frequency

Circuit breakers of up to 600 amperes can be applied to frequencies of 50-120 Hz. A frequency higher than 120Hz will cause the circuit breaker to have to be derated. In higher frequency projects, eddy currents and iron loss will cause greater heat generation in the thermal trip assembly, so the circuit breaker needs to be derated or specifically calibrated. The total amount of derating depends on the ampere rating, frame size, and current frequency. The general rule of thumb is that the higher the ampere rating in a particular frame size, the greater the derating required.

 

All higher rated circuit breakers over 600 amperes contain bimetallic strips heated by the transformer and are suitable for AC power up to 60 Hz. For minimum AC applications at 50 Hz, special calibrations are usually available. The solid-state trip circuit breaker is pre-calibrated for 50Hz or 60Hz applications. If you do a diesel generator project, the frequency will be 50Hz or 60Hz. Before advancing the 50Hz project, it is best to check with the electrical contractor in advance to ensure that the calibration measures are in place.

 

3. Maximum interruption capacity

The breaking rating is generally considered to be the maximum amount of fault current that the circuit breaker control panel circuit breaker can break without causing the system itself to malfunction. The maximum amount of fault current provided by the system can be calculated and determined at any given time. An absolutely reliable rule that must be followed when applying the correct circuit breaker. That is, the breaking capacity of the circuit breaker must be equal to or greater than the amount of fault current that can be transmitted at the point where the circuit breaker is applied in the system. Failure to apply the correct amount of breaking capacity will result in damage to the circuit breaker.

 

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4. Continuous rated current

Regarding the continuous current rating, molded case circuit breakers are measured in amperes at a specific ambient temperature. The ampere rating is the continuous current that the circuit breaker will carry at the calibrated ambient temperature. The general rule of thumb for circuit breaker manufacturers is to calibrate their standard circuit breakers at 104°F. The ampere rating for any standard application depends only on the load type and duty cycle. The ampere rating is managed by the National Electrical Code (NEC) and is the main source of load cycle information for the electrical contracting industry. For example, lighting and feeder circuits usually require circuit breakers rated according to the current carrying capacity of the conductors. To find various standard circuit breaker current ratings and allowable loads for different sizes of conductors.

 

5. Atypical operating conditions

When choosing a circuit breaker, it is important to keep in mind the location of the end user. Each circuit breaker is different, and some are more suitable for more ruthless environments. When deciding which circuit breaker to use, please keep the following in mind.

 

(1) High ambient temperature: If the standard thermal magnetic circuit breaker is used at a temperature exceeding 104°F, the circuit breaker must be derated or recalibrated to adapt to the environment. For many years, all circuit breakers have been calibrated to 77°F, which means that all circuit breakers above this temperature must be derated. In fact, the temperature of most enclosures is around 104°F. A common special circuit breaker is used in these types of situations. In the mid-1960s, industry standards changed, and all standard circuit breakers were calibrated with 104°F in consideration.

 

(2) Corrosion and moisture: In an environment with constant humidity, it is recommended to perform special moisture-proof treatment on the circuit breaker. This treatment helps fight mold or fungus that can corrode the equipment. In high humidity environments, the best solution is to use a space heater in the enclosure. If possible, remove the circuit breaker from the corroded area. If this is not practical, a specially manufactured corrosion-resistant circuit breaker can be used.

 

(3) High impact probability: If the circuit breaker is to be installed in an area with a high possibility of mechanical impact, a special anti-impact device should be installed. The anti-vibration device consists of an inertial weight on the center rod, which is used to lock the trip rod under normal vibration conditions. The weight should be installed so that it will not prevent the thermal or magnetic release from functioning under overload or short-circuit conditions. The U.S. Navy is the largest end user of the high seismic breaker required by all warships.

 

(4) Altitude: In areas above 6,000 feet above sea level, the current-carrying capacity, voltage and breaking capacity of the circuit breaker must be derated. At high altitudes, thinner air does not conduct heat away from current-carrying components and denser air at lower altitudes. In addition to overheating, the thin air prevents the dielectric charge from building up fast enough to withstand the same voltage levels that occur at normal atmospheric pressure. Elevation issues can also degrade the ratings of most generators and other power generation equipment used. It is best to talk to a power generation professional before buying.

 

(5) Installation position: In most cases, the circuit breaker can be installed in any position horizontally or vertically without affecting the tripping mechanism or breaking capacity. In areas with strong winds, the circuit breaker must be installed in the enclosure (most devices are enclosed), and the surface will sway with the wind. When the circuit breaker is connected to an inflexible surface, it may damage the circuit when exposed to high winds.

 

6. Maintenance and testing

Circuit breaker maintenance and repair When choosing a circuit breaker, the user must decide whether to purchase equipment that has passed UL testing (Underwriters Laboratories). In order to ensure the overall quality, it is recommended that customers purchase UL-tested circuit breakers. Please note that products not tested by UL cannot guarantee the correct calibration of the circuit breaker. All UL-certified low-voltage molded case circuit breakers are tested in accordance with UL standard 489, which is divided into two categories: factory test and field test.

 

(1) UL factory test: All UL standard molded case circuit breakers have undergone extensive product and calibration tests based on UL standard 489. UL certified circuit breakers include a factory seal calibration system. The complete seal ensures that the circuit breaker is properly calibrated and has not been tampered with or changed, and the product will operate in accordance with UL specifications accordingly. If the seal is broken, the UL guarantee and any guarantee are invalid.

 

(2) Field test: It is normal that the data obtained on the site is different from the published information. Many users are confused about whether the field data is flawed or the published information is out of sync with their specific model. The difference in data lies in the fact that the test conditions in the factory are quite different from those in the field. Factory testing is designed to produce consistent results. Temperature, altitude, climate control environment, and the use of test equipment specifically designed for the product under test will all affect the results. Some circuit breakers have their own test instructions. If there are no instructions, please use a reliable circuit breaker service company.

 

(3) Maintenance: In most cases, molded case circuit breakers have an excellent reliability record, which is mainly due to their closed devices. The housing minimizes the risk of contact with dirt, moisture, mold, dust, other containers and tampering. Part of proper maintenance is to ensure that all terminal connections and trip units are tightened to the correct torque values set by the manufacturer. Over time, these connections will loosen and need to be re-tightened. The circuit breaker also needs to be cleaned regularly. Incorrectly cleaned conductors, wrong conductors for terminals, and loose terminals are all conditions that can cause the circuit breaker to overheat and weaken. Manually operated circuit breakers only need their contacts to be clean and the connecting rods to be freely operable.

 

Jiangsu Starlight Electricity Equipments Co.,Ltd. is a diesel generator set manufacturer with more than 40 years of production experience. Its main brands include Yuchai generator sets, Cummins generator sets, Volvo generator sets, etc., and 64 sales and service departments nationwide. Users provide one-stop service of design, supply, debugging and maintenance. Welcome contact us by email sales@dieselgeneratortech.com


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