What Is an Emergency Power System?

The emergency power supply system is an emergency power supply that meets special requirements such as the fire protection industry. Emergency power is widely used in various construction projects as a backup power source independent of the power grid. Currently emergency power sources include diesel generators and batteries. In recent years, EPS with batteries has been widely used as emergency power sources, especially by Used as a fire emergency power supply. Its working principle is the use of single inverter technology dual power supply for emergency, the advantages are automatic switching, strong load capacity.

Emergency power system

With the development of society and the continuous improvement of the level of building technology, urban buildings tend to be large-scale, and the development of high-rise buildings will require higher and higher power supply. The informationization of society and the modernization of buildings will make buildings The dependence on power supply is also increasing, especially for some important public buildings. Once the power supply is interrupted, it will cause significant political impact or economic loss. If a fire occurs, the consequences are even more unimaginable. Therefore, the current "Fire Protection for High-rise Civil Building Designs" The "Code" and "Code for Electrical Design of Civil Buildings" have strict regulations: "The first-level load should be powered by two power sources. When one power source fails, the other power source will not be damaged at the same time. The particularly important load in the first-level load, In addition to the above two power sources, an emergency power source must be added. Common emergency power sources are: (1) a generator set independent of the normal power source; (2) a dedicated power supply line effectively independent of the normal power source in the power supply network; (3) "Battery." Over the years, operating experience has shown that the grid uses two independent power sources. If the main power supply line is out of power, the backup power supply is used. Although this method is simple and reliable, the power supply line is complicated. When a large-scale power outage occurs, both power sources may have a power outage.

The emergency power supply adopts single inverter technology, which integrates charger, battery, inverter and controller. The battery detection and shunt detection circuits are designed inside the system, and the backup operation method is used.

When the mains power is normal, the mains power is supplied to the important load through the mutual investment device, and the mains power detection and battery charging management are performed, and then the battery pack provides DC energy to the inverter. Here, the charger is a It is necessary to provide the battery pack with a low-power DC power source with a charging current equivalent to 10% of the battery pack capacity (Ah). It does not have the ability to provide DC power directly to the inverter. At this time, the mains power is passed through the EPS bypass bypass. The power supply system composed of the transfer switch and the switch supplies power to various emergency loads of the user. At the same time, under the control of the EPS logic control board, the inverter stops working and is in an automatic shutdown state. Under this condition, the user load is actually used The power source is the commercial power from the power grid. Therefore, EPS emergency power supply is also always said to be in sleep state, which can effectively achieve energy saving effects.

When the mains power supply is interrupted or the mains voltage exceeds the limit (± 15% or ± 20% of the rated input voltage), the mutual investment device will immediately switch to the inverter to supply power, supported by the DC energy provided by the battery pack At this time, the power used by the user load is AC power converted by the inverter of the EPS, not from the mains.

(3) When the mains voltage returns to normal operation, the EPS control center sends a signal to perform an automatic shutdown operation on the inverter, and also performs a switching operation from the inverter power supply to the AC bypass power supply through its transfer switch. Thereafter, the EPS While supplying AC power to the load via the AC bypass power supply path, the battery pack is also charged through the charger.

2.How to choose EPS

EPS usually has the following product characteristics:

EPS power is 0.5 ~ 10KW

It is composed of single and dual power supply input products (input voltage 220Vac or 380Vac, output voltage 220Vac), suitable for lighting loads for emergency lighting and accident lighting.

(2) EPS power is 2.2 ~ 400KW

It consists of single and dual power supply input products (input voltage 380Vac, output voltage 380Vac). In addition to emergency lighting and accident lighting, it is also suitable for fire elevators, shutter doors, fans, water pumps, shower pumps, water supply pumps, etc. Inductive load or hybrid power supply.

(3) EPS power is 2.2 ~ 400KW

It consists of three types of products: single inverter single load, single inverter single load, one backup, dual inverter single load, one backup and one backup (input voltage 3800Vac, output voltage 380Vac), which are only for fire protection with only one power supply. The electric motor in the facility or the first-level load provides a variable-frequency three-phase emergency power supply system, which can solve the emergency power supply of the electric motor and the impact on the power supply equipment during the startup process without any starting device between the power supply and the motor. Motor loads such as elevators, central air conditioning, fire pumps, etc. in high-rise buildings.

According to the load characteristics of the product, how to choose the EPS you need and the points to pay attention to:

2.1 EPS (1 ~ 50KVA) for emergency lighting or accident lighting

According to GB17945-2000 national standard (fire emergency lighting), in order to ensure that the building's emergency lighting system can operate normally, the EPS has the following basic requirements:

(1) It is required to be responsible for the power supply interruption time of EPS to ordinary emergency lights <5s. However, for emergency lighting in high-risk work areas and critical work areas, the power supply interruption time of EPS is required to be <0.25s.

(2) In order to use the city power as much as possible, when the mains voltage is within the range of 187 ~ 242V (220V, -15%, + 10%), EPS is not allowed to enter the inverter power supply state.

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

(4) The maximum charging time of the battery pack by the charger in EPS is less than 24H, and the maximum charging current is less than 0.4C (A)

When the mains power supply is normal, the EPS supplies power to the load through its AC bypass. In principle, it can carry loads with various power factors. However, when the mains power supply is interrupted or the mains voltage or frequency exceeds the limit, then It is powered by an inverter in EPS. Under this condition, the load capacity of EPS not only needs to consider the derating output characteristics of the inverter when the power factor value is different. It also needs to be based on the emergency used. The output power and model of the EPS are selected according to the different lighting fixtures. The following issues should be noted when selecting the EPS:

(1) Ordinary emergency lighting fixtures. Because the power consumption of emergency lighting is marked with active power P (KW), the output power of EPS inverters is the apparent power when the power factor cos = 0.8 (lag). S (KVA). So, the full load output power of the EPS should be: S = P / 0.8.

(2) When the emergency lighting fixture is a fluorescent lamp, the selected EPS full-load output power should be S = (1.3 ~ 1.5) P / 0.8. The reason is that there is a large "starting surge" current when the fluorescent lamp starts.

(3) When the emergency lighting is a high-pressure gas lamp (for example: high-pressure sodium lamp, high-pressure palladium lamp, etc.), EPS products with a switching time of less than 20ms should be selected. This is because if the power supply interruption time for the high-pressure gas lamp exceeds 20ms, It may cause the discharge arc in the gas lamp to "extinguish or be interrupted". Once the interruption of the discharge arc occurs, even if the power is restored immediately, it may cause the lamp to go out for several minutes. This is because it takes a long time to re-predict The reason for the filament in the hot high-pressure gas lamp. Obviously, this kind of failure is not allowed for the lighting system of large stadiums and performance venues.

2.2 EPS (Three-phase, 5 ~ 400KVA) for emergency lighting + motor mixed load

In order to correctly select the output power of the EPS, the ratio of the resistive lighting load to the inductive electromechanical load should be calculated separately. For the motor load, due to the different models and working methods selected by the user, its starting current may be as high as 5 to 10 times the rated operating current. To ensure the safe operation of the motor and the EPS itself, for this part of the motor load, not only the selected EPS output power should be more than 6 times the nominal power of the motor. Moreover, it should also be selected EPS models whose switching time is less than 15ms.

2.3 EPS with motor load

(1) Adopting the hard start of the motor: The working mode, the selection scheme for this EPS output power is the same as described in 22. The advantage of using this scheme is that no matter when the mains power supply is interrupted or when the mains power resumes normal work, EPS can ensure the continuous operation of the motor. The disadvantage is that high-power EPS is required and the cost is high.

(2) Use motor-specific EPS with variable frequency start function

When the mains power supply is normal, power is supplied to the motor load via the AC bypass and transfer switch. At the same time, the mains power is also charged to the battery pack via the charger. When the mains power supply is interrupted, in order to ensure the safe operation of the EPS, he hopes that "Time-delay switching" operation, in order to make the motor stop completely and then start the inverter, and it will perform the operation of frequency conversion starting from 0 ~ 220Hz to the subsequent motor (starting time is a few seconds). The benefits of the launch plan are:

Prevent applause caused by the self-excitation power generated by the EPS and the motor in the "inertial motion state" being in an "asynchronous lock-in" state;

It can reduce the output power of the EPS and reduce the investment cost. At this time, the output power of the EPS only needs to select 1.2 to 1.4 times the rated power of the motor to meet the requirements.

The disadvantages are:

The user's motor load is required to stop first, and then "frequency start" at full speed, thus causing "discontinuity" in the motor load operation.

If the following motors need to perform "time-sharing start" operation at different times, you may encounter such technical difficulties: when starting the motor in a stationary state, if the output power of the EPS is large enough, it may withstand 5 ~ 10 times the impact of the motor starting surge current. Otherwise, it will force the EPS to enter a new round of "frequency conversion start" working state. One of the problems caused by this is: the motor that was originally at the normal working speed It will re-enter the variable-speed start-up phase from 0 to 50 Hz, which will cause trouble for the user's work.

3.The difference between EPS and UPS

3.1. The backup UPS supplies power to the load directly from the mains when the mains is normal. When the mains exceeds its working range or is powered off, the UPS is switched to battery inverter power supply via a transfer switch. Its characteristics are: simple structure, small size, low cost, but narrow input voltage range, poor stability of output voltage stability, switching time, and the output waveform is generally square wave

3.2. The online interactive UPS supplies power to the load directly from the mains when the mains is normal. When the mains is low or high, it is output by the internal voltage stabilization line of the UPS. The switch turns on battery power. Its characteristics are: a wide input voltage range, low noise, small size and other characteristics, but there is also switching time.

3.3. When the mains power is normal, the online UPS rectifies the mains power to provide DC voltage to the inverter, and the inverter provides AC power to the load. When the mains power is abnormal, the inverter is powered by the battery and inverter The device is always in working condition to ensure uninterrupted output. Its characteristics are that it has a very wide input voltage range, basically no switching time, and high stability of output voltage stability. It is especially suitable for occasions with higher power requirements, but the cost is higher. At present, UPSs with powers greater than 3KVA are almost all online UPSs.

The UPS also has the functions of voltage stabilization and filtering. Some UPSs can be powered by the mains bypass in case of failure or overload.

The backup voltage output has large fluctuations. Between 170V-260V, high-speed relays are used to achieve the conversion between the mains and the battery, and the conversion time is less than 10 milliseconds. The on-line type always uses the inverter circuit to work, and its voltage stability is high, which is basically in the range of 220V ± 5%, and there is basically no conversion time for the battery; the static switch is used for the mains bypass conversion, and the conversion time can reach microseconds. level.

UPS has high output accuracy, fast conversion time, and high cost (about twice the EPS), usually has large energy consumption (online), and has a short lifespan (8-10 years).

EPS is a bit similar to a backup UPS. Usually the inverter does not work, and the battery is only put into operation when the mains power fails. Generally, no constant current or constant voltage treatment is performed on the power supply. Contactor conversion is usually used, and the switching time is 0.1 ~ 0.25S. Its advantages are simple structure, low cost, low energy consumption and no noise, long life of the host (15-20 years), can be adapted to inductive, capacitive and comprehensive loads, and can realize variable frequency soft start when needed.

"EPS and UPS for Emergency Power" Li Chengzhang

GB17945-2000 national standard (fire emergency lighting)

(1) When the power grid is powered, it is static and no noise; when powered, the noise is less than 60dB. No need for smoke exhaust and anti-shock treatment, and it has the characteristics of energy saving, no pollution, and no hidden danger of fire;

(2) Automatic switching, which can realize unattended operation. The switching time between the grid power supply and the EPS power supply is 0.1 0.25s;

(3) Strong load capacity, EPS is suitable for inductive capacitive and comprehensive load equipment, such as elevators, water pumps, fan office automation equipment, emergency lighting, etc .; (4) Reliable use. The life of the host is more than 20 years; (5) Adapt to harsh environment. It can be placed in the basement or power distribution room, or it can be set up close to the place of emergency load to reduce the power supply lines.