Detailed explanation of fire emergency power supply EPS

　　EPS uses the mature inverter technology of UPS circuits. They both have the function of continuing to provide AC power to the load in the event of a mains failure (interruption). The difference is that UPS is always powered by the inverter output to ensure the power quality, while the inverter of EPS is in the start-up state when the mains power is normal, but it does not output power. The mains power is bypassed by the inverter output to ensure emergency power supply in the event of a mains failure.

　　UPS mainly provides power supply for IT industry equipment, while EPS is suitable for various industries; the UPS power supply mode requires a very short switching time (0-10ms), while EPS is relatively wide (0-4s); UPS mainly carries computer loads, while EPS carries more mixed loads; UPS has high requirements for the operating environment, while EPS requires to adapt to various environments; UPS is mainly used for general user monitoring, while EPS is mainly used for emergency power supply and requires linkage with fire protection; UPS is mainly aimed at maintaining smooth information transmission, while EPS is mainly aimed at preventing major accidents.

　　At present, EPS can be roughly divided into the following three types according to the type of load it carries: the first is EPS mainly used for emergency lighting (mostly single-phase); the second is a three-phase series EPS used for inductive loads such as air conditioners, elevators, rolling doors, exhaust fans, water pumps, etc. in addition to emergency lighting, or a mixed power supply of both; the third is a variable frequency series EPS that directly supplies power to the motor and is only used as a backup power supply for the emergency lighting system. The first type of EPS mentioned above is generally selected. In order to ensure the normal operation of the emergency lighting system, the following basic requirements are put forward for EPS switching time and continuous working time in accordance with the technical requirements of "Fire Emergency Lighting" (GB17945-2000):

　　1) The power supply interruption time of EPS responsible for supplying power to ordinary emergency lighting is required to be less than 5s. However, for emergency lighting in high-risk work areas and key work areas, the power supply interruption time of EPS is required to be less than 0.25s.

　　2) Use AC power as much as possible. When the AC voltage is within the range of 187-242V, EPS is not allowed to enter the inverter power supply state.

　　3) EPS is required to be equipped with a battery pack of sufficient capacity to ensure that the emergency lighting can continue to work for at least 90 minutes when the mains power supply is interrupted.

　　4) The maximum charging time of the battery pack in the EPS charger shall not exceed 24 hours, and the maximum continuous overcharge current shall not exceed 0.05C5A. For mixed loads (inductive loads such as lighting, motors, or both), the switching time of the EPS should be less than 12ms. The ratio of resistive lighting loads to inductive electromechanical loads should be calculated first; when calculating inductive electromechanical loads, the current impact when the motor starts should be considered:

　　1. For electric motors without any frequency conversion or reduced voltage starting, the capacity should be calculated as 5-10 times the motor capacity.

　　2. For motors with star/delta reduced voltage starting, the capacity should be calculated as 3 times the motor capacity.

　　3. For motors with soft start, the capacity should be calculated as twice the motor capacity.

　　4. For motors with variable frequency starting, the capacity is calculated as 1.2-1.4 times the total motor capacity.

　　In order to ensure the normal operation of other fire-fighting equipment except emergency lighting in the event of an accident, the following basic requirements are put forward for the continuous working time of EPS in accordance with the requirements of the "Civil Building Electrical Design Code":

　　1. Enable water spray and foam fire extinguishing systems to continue working for more than 30 minutes

　　2. The fire accident broadcast system can continue to work for more than 20 minutes.

　　3. Various alarms and warning devices shall work continuously for no less than 10 minutes.

　　4. Fire elevators, smoke exhaust equipment, etc. continue to work for more than 60 minutes.

　　EPS can be placed in a basement or main distribution room, or arranged in a small distribution room or even in a building shaft, or can be set up close to the emergency load use site to reduce power supply lines. The EPS should be placed in a place with good ventilation and heat dissipation or have corresponding ventilation and heat dissipation measures.

As a reliable green emergency power supply, 　　EPS has been used more and more widely. I believe that in the near future it will have newer products that are more mature and reliable. We should learn about it in time so that we can use it freely in fire protection design according to different usage scenarios and make our lives safer.