ESM1-63 3P

In photovoltaic systems, the selection of AC circuit breakers is a matter that cannot be overlooked. If the circuit breaker is not compatible, it may cause frequent tripping, overheating damage, and even system fires. Especially in summer, high temperatures can easily lead to frequent false trips of the circuit breaker. Let’s discuss the key points to consider when choosing a circuit breaker in a photovoltaic system, and take a photovoltaic power station designed with five G5-GC60K inverters as an example for selection calculation and correction analysis.

Circuit Breaker Selection Principles:

DC Breaker2

 

In solar photovoltaic systems, the choice of circuit breakers depends on the following factors:

➤ Electrical characteristics of the system;

➤ Working environment;

➤ Load and installation requirements.

  1. Ambient temperature:

DC

Equipment in photovoltaic systems is usually installed outdoors. When the outdoor temperature is high, the temperature inside the distribution box will be higher, which will affect the current capacity and working temperature of the circuit breaker. Therefore, temperature is the primary consideration in the selection of circuit breakers in solar photovoltaic systems. According to IEC60947-2 standards, each circuit breaker has a detailed table or temperature compensation curve indicating the ambient temperature derating/increasing current values. In actual installations, the rated current value of the selected circuit breaker should be corrected based on the site’s ambient temperature and system current size.

  1. Multiple circuit breakers installed side by side:

MCCB

For large-scale solar photovoltaic systems with multiple inverters, the distribution box usually has multiple circuit breakers installed closely together. When these circuit breakers work, their temperature rise will more quickly affect each other, which may cause premature tripping.

Therefore, when multiple circuit breakers are installed side by side in a distribution box, we need to consider the correction factor. This factor will be specified in the circuit breaker’s data sheet.

If eight adjacent miniature circuit breakers S201-C16 are installed at an ambient temperature of 40℃; Circuit breaker rated current ln = 65a; At an ambient temperature of 40℃, the maximum working current = 15.1A, factor F = 0.75; ln = 0.75 x 15.1A = 11.33A; Through calculation, it can be found that the working current can only be increased to a maximum of 11.33A.

If the current value is too small, we can use a circuit breaker with a higher rated current. Alternatively, we can increase the gap between circuit breakers to reduce the temperature rise impact on each other and prevent unnecessary tripping.

  1. Type of connected equipment:

When connected to the grid, the photovoltaic system will be affected by the current and voltage fluctuations of the grid load feeder network. In choosing a circuit breaker, the composition of the grid load also needs to be considered in order to select the most suitable circuit breaker. Reference standards: IEC60898, IEC60947-2, GB10963.1.

 

Taking as an example a photovoltaic power station designed with 5 G5-GC60K inverters, their technical specifications can be referred to the G5-GC60K inverter specifications:

DC Breaker1

• Rated output current = 91.2A

• Maximum output current = 100A Environmental temperature, installation method, and load conditions significantly affect the selection of circuit breakers.

➤ Circuit Breaker Selection and Verification

 

DC Breaker

By calculating the inverter’s maximum current, we typically base our circuit breaker selection on 1.2 to 1.5 times the rated current. Thus, with motors and transformers as loads, we chose a 125A circuit breaker with D thermal release characteristics based on the calculated current of 91.2A, assuming no gaps between the circuit breakers during installation.

Next, we verify the suitability of our chosen value by checking the circuit breaker’s thermal adaptability:

Load factors:

• Permanent load duration > 1h = 0.9 (The photovoltaic power station may experience permanent loads for more than 1 hour)

• Circuit breaker arrangement reduction factor = 0.8 (If using a single circuit breaker or having sufficient distance between two circuit breakers, the factor equals 1)

• Environmental temperature correction factor = 1.0 when the environmental temperature is 40℃

微信截图_20230330144001

Conclusion: In non-fault high-temperature operation, when the circuit breaker’s maximum current-carrying capacity is less than the inverter’s maximum output current, the circuit breaker will trip.

 

Circuit Breaker Tripping Solutions

Tripped circuit breakers can be resolved in two ways:

➤ Solution 1 Continue using the 125A circuit breaker.

With sufficient heat dissipation space (>10mm) between the circuit breakers, the maximum current-carrying capacity is 101.25A (Ibn = 50A x 0.9 x 0.9 = 101.25A); the circuit breaker will not trip during rated operation.

➤ Solution 2:

Use a 150A circuit breaker. The maximum current-carrying capacity is 108A (Ibn = 150A x 0.8 x 0.9 x 1 = 108A); the circuit breaker will not trip during rated operation.

If you are interested in this article or have any questions, please consult: concact@onccy.com