Backup Power: Generator Selection And Installation

• Generator types
• Determination of priority consumers and plant capacity
• Arrangement of the generator room
• Connection to the home power supply
• Related Videos

Generator types

The choice of portable power plants in the domestic market is very wide. Most of the products are represented by clones of the same type, which are well suited for powering a power tool when working on the road, but using such equipment for backup power supply at home would not be the best idea. There is an impressive list of differences: efficiency, noise level, engine life, operating time without downtime, purity of the output voltage and power control circuit. A separate generator unit is responsible for each of these parameters, so understanding the details of the device is imperative for choosing the right backup power source.

The engine is the main and most important part of an autonomous power plant. Three types of motors can be used in home generators:

Gasoline internal combustion engine. It is most widely distributed due to the simplicity of the device, at the same time it is characterized by the lowest efficiency, but at the same time it is cheap to maintain. Most gasoline generators are not capable of operating for a long time without stopping, so the choice in their favor should be made only if power outages are rare and short-lived

The diesel power unit is characterized by a reduced noise level, while the unevenness of the stroke under load and without it is much less than that of a gasoline one. Continuous operation is permissible. It is believed that it is advisable to use a diesel power plant with a power of more than 16 kW, which is refuted by the successful experience of operating diesel generators with a capacity of 4 kW or more. Completing a power plant with a diesel engine in a number of cases makes its operation up to 40% more economical in comparison with a gasoline engine, however, if a high-speed engine is used, its operation without load greatly reduces the service life, which, although higher than that of gasoline installations, is much more complicated

A natural gas engine is an analogue of a gasoline engine that uses mainline or liquefied blue fuel as fuel. The main advantage is high efficiency: the cost of a kilowatt of generated electricity can be up to 10 times lower in comparison with a gasoline generator when using main gas and 5-7 times lower when using liquefied gas. At the same time, the fuel system of such engines is more complicated, and connection to the gas main requires a change in the gas supply project with all the ensuing safety requirements for the operation of gas equipment

An electric generator is part of a power plant that converts rotational kinetic energy into alternating current. At the moment, synchronous generators with an electronic excitation system are considered the most suitable for use in backup power supplies, which allow adjusting the voltage on the fly, providing a limiting difference of 2-3% of the nominal values. Providing a stable sine wave for connecting power-sensitive equipment (office equipment, boilers, refrigerators) in generators is achieved by using inverter converters.

The choice of the number of generator phases is not obvious. A three-phase source should be preferred only if the load is evenly distributed over the phases, as a rule, the permissible imbalance for generators is no more than 15–20%. Otherwise, it is better to choose a single-phase generator of higher power.

Determination of priority consumers and plant capacity

The redundant power line does not have to be connected to the entire power grid. Provided that a selective protection scheme is implemented on the input distribution board, it is possible without significant efforts to connect only those consumers for whom uninterrupted power supply is critically important or at least preferable.

First of all, backup power should be supplied to the building's life support systems. These include a boiler room, a pumping station, a central forced ventilation unit, exhaust fans for bathrooms and technical rooms. Secondary priority is given to the lighting network: with a sufficiently low energy consumption of modern light sources, the lighting in the house can be connected to the backup power entirely. It is also desirable to ensure the smooth operation of the home telecommunications network and security systems, which include a modem, wireless network and network storage, video surveillance, fire and burglar alarms. The consumption of these devices is relatively low, but their shutdown for a long time can promise serious inconvenience.

Household consumers need an uninterrupted power supply for a refrigerator, microwave oven, home theater, workplaces with personal computers. Also, it will not be superfluous to allocate several outlet lines for charging mobile devices and general needs. With limited generator power, you should not provide emergency power to household appliances with significant consumption: washing machines, water heaters, an electric stove and an oven.

In general, the minimum generator power is determined by the aggregate of consumers of the first (life support) and second (lighting, telecommunications) groups based on their simultaneous operation. The additional power reserve is determined by the nature of the work of consumers of the third group, taking into account the frequency of their activation. It should be remembered that the current consumption at start-up may differ from the nominal: for devices with electronic power supplies and collector motors up to 500 W, 2–2.5 times, for refrigerators and pumps with asynchronous motors - up to 3–5 times. This feature must be taken into account both when choosing the generator power and during the operation of the backup power line. The generator power must be 15-20% higher than the aggregate rated power to prevent the equipment from operating at full load.

Arrangement of the generator room

The presence of a specially equipped platform for the generator is not necessary, but significantly increases the usability and fault tolerance of the backup source. The main benefit of a stationary installation is the ability to put the generator into operation by literally pressing a couple of buttons without laying a temporary cable. In addition, the operation of the generator will be possible in any weather, including at extremely low temperatures.

To accommodate the generator, even a small extension to the house is suitable - a metal frame sheathed with a profiled sheet. It is optimal if a cement screed with mortgages for fastening the generator frame is poured on the floor. To reduce the noise level and maintain an acceptable temperature inside, it is recommended to fill the frame walls with mineral wool, having previously fixed the vertical wooden lathing. To protect the filler, it is advisable to make the inner lining with thin materials: plywood or MDF.

A backup line cable with an appropriate cross-section of conductors must be brought into the generator room. Since the vast majority of generators are grounded in an isolated neutral circuit, a single-phase installation will require two conductors, and a three-phase installation three. The protective conductor is wound directly from the ground loop and connected to the generator frame. An exhaust system is not required as such if the extension is sufficiently distant from windows and ventilation ducts. In other cases, it is recommended to install a galvanized pipe with an accelerating section of about 4–5 meters, into the lower part of which a corrugated metal sleeve is inserted, connected to the generator exhaust pipe. It is not necessary to seal the connection, with natural draft, the exhaust gases will be completely removed, carried away by the upward flow.

Connection to the home power supply

The final stage of installation is the assembly of the wiring diagram. It is imperative to provide protection against the simultaneous connection of two lines, for which it is convenient to use modular switches of the TDM MP-63 type for single-phase networks or reversible modular switches of the ABB OT63E3C type for three phases. Also, as a budget solution for single-phase networks, you can offer a pair of identical two-pole machines: one of them is installed in an inverted position, then the flags are connected with a pin. It is imperative that, during switching, a break is ensured not only of the phase conductors, but also of the working neutral.

The connection of the reserve line to the distribution network must be carried out between the main switch and the common power bus, to which the protective devices of the individual lines are connected. In this case, the backup line must be connected bypassing general protective devices: RCD and differential protection, voltage relay, SPD and lightning arresters. If a single-phase generator is connected to a three-phase network, the three-phase RCDs will not work, so the backup line must be connected bypassing them. Single-phase RCDs of selective protection will work as expected.

Connecting the generator through a three-position switch: 1 - input circuit breaker; 2 - counter; 3 - RCD; 4 - generator; 5 - three-position switch; 6 - zero bus; 7 - grounding bus; 8 - to consumers

If the generator has a starting system with an electric drive, it is recommended to replace the ASU with a special generator automation panel. It contains an automatic transfer switch with an adjustable time delay between starting and connecting the load, starting control and all the necessary protections. In the absence of an automatic start system, it is carried out manually: first you need to switch to the backup line, turn off the machine on the generator, connect the connecting cable to the outlet, start the engine and wait until the speed stabilizes. Switching on the circuit breaker on the generator when starting manually is always done last, and when stopped first.

Scheme of automatic transfer of reserve: 1 - input automatic machine; 2 - counter; 3 - RCD of the main network; 4 - block for automatic generator start; 5 - generator; 6 - RCD of the reserve network; 7 - time relay; 8 - main input contactor; 9 - contactor of reserve input