Emergency power system

A power generator ( emergency generator ) is a device that generates electricity from existing resources, in particular, to be independent of power grids. A drive unit, usually an internal combustion engine ( eg, diesel or gasoline engine ) and a generator to produce electricity in this case form a unit.

In special cases, emergency generators also be driven electrically, eg by rail power transform with non-matching frequency in appropriate emergency.

Such mobile or stationary devices can all be found in applications where the public power supply is missing ( " Generator " ) or the failure of the mains ( German black case, english blackout. ) Would lead to serious consequences - for example, in hospitals, chemical plants, server rooms, and not least in nuclear power plants to even in the event of disconnection or failure of the power grid to ensure the decay heat removal.

  • 4.1 Stationary Use
  • 4.2 Mobile application
  • 4.3 -board power supply
  • 4.4 scooters

General

Generating sets ensure the availability of electrical energy independently from the electricity grid, and are often referred to as " emergency generator " or - aggregate, more powerful devices as power systems (NEA ).

Size and performance of such emergency generators differ significantly. It starts with small portable devices that are sufficient to power small appliances (refrigerator / freezer / PC) or an emergency lighting system, and goes beyond mobile NEA of THWs on truck trailers to large, permanent installations with several thousand kVA.

Normally NEA can maintain the supply of their performance corresponding number of electricity consumers permanently, but not feed power into the public grid ( this mode is called isolated operation). Is this still the case, it must be ensured that there is no unsynchronized regeneration occurs.

If the unit is equipped with an appropriate control, may, after termination of the power failure, the so-called net return on the public network synchronized again and the unit will shut off, causing an interruption is avoided in the downshift.

If the emergency power system does not have a UPS (uninterruptible power supply), it comes in a failure of the public network so long an interruption until the unit has reached the required operating parameters and can take over the power supply. In devices for applications according to VDE 0100-710 and VDE 0100-718 certain time limits for the provision of emergency power may be prescribed.

Also causes a short-term power interruption lasting damage, the emergency power system of an uninterruptible power supply (UPS ) must be supported, which takes over the power after the power failure for a few minutes until the emergency power plant is ready to produce constant current. Uninterruptible power supplies require especially hospitals, sensitive technical or chemical plant control systems for the continuous control of critical processes, network nodes (hubs ), server rooms and data centers.

Emergency case

The " emergency case " is to maintain the electrical power supply in case of failure of the power grid by one or more emergency generators. This can be done manually or automatically. The automatic start and automatic load switching are mandatory for all systems for which a power system was required by law. The NEA can not be replaced by multiple connections to different power grids of different energy suppliers, as a failure of a power grid may lead to a domino effect that overloading and failure of adjacent grids by itself.

According to statistics from the GRS, there have been six emergency cases in German nuclear power plants between 1993 and 2006: In Gundremmingen C on May 8, 1993 in Neckarwestheim 1 on 12 May 1999, the same location again on 4 June 2000 in Grafenrheinfeld on 2 April 2002, Biblis B on February 8, 2004, for a third time in Neckarwestheim 1 on 19 February 2005.

Technology

Energy sources

Smaller units are usually powered by a gasoline engine, greater contrast with diesel engines. Otto fuel is more difficult to handle in terms of explosion protection and is therefore inadmissible building regulations for stationary units.

Be started generating sets by cable, by means of compressed air or electric start, with the last possibility requires the presence of a battery. In nuclear power plants, the start is done automatically by the reactor protection system.

In the agricultural field can be found so-called PTO shaft generators which are connected to the power take-off, or the PTO shaft of a vehicle. This PTO generators not have their own motor but are driven via an intermediate gear and a shaft of a tractor (tractor ). This has the advantage that these devices are cheap to purchase and maintain, as to be purchased and maintained no combustion engine.

In the meantime, hydraulic driven generators are available up to 70 kVA, which can be driven by an on-board hydraulic system. Fuel cell power packs are already commercially available, but not very common and very expensive.

Generator

As generators for generating sets both synchronous and asynchronous machines are used. Asynchronous machines can hold up to powers of about 2.5 kVA use, beyond synchronous machines. Since induction machines do not provide reactive power in island operation without special facilities, only resistive loads ( eg heaters or lighting equipment) can be fed into the case. Synchronous machines have an excitation device, and are thus in the isolated operation in the ability to supply reactive power for capacitive or inductive loads in addition to the active power to resistive loads.

Operational safety

A delicate question is particularly important for mobile devices always whether sufficient ground exists, so that no current can accidents happen. It is often dependent on which protective measures (fuses, circuit breakers or insulation monitor ) are connected between the emergency generator and the consumer. As long as individual consumers of the operating instructions are connected accordingly, the security is ensured. Since 2007, may be used with insulation monitoring in Austria in agriculture only generators. An insulation monitoring makes the earthing spike superfluous and is safer. With a residual current device (RCD ), a ground resistance must be achieved, which is small enough so that the RCD trips. In a rocky or sandy soil that is not possible.

Connection to the public grid

Most dispatching for economic reasons is not allowed or restricted, for example, for residential customers by statutory requirements. Furthermore, there is a high hurdle, namely the necessary synchronization, this requires an additional technical effort. For feeding power systems are used, which can be synchronized with the grid.

Emergency power supplies have prescribed facilities such as mains dip relay, with which they can be connected to the normal building power supply, but then (apart from systems that are designed for Kurzzeitparallebetrieb after return of power in the normally serving network ) can not provide power to the public grid. The exact requirements will depend on the requirements of the network operator ( power company ) and of the device description.

Use

Stationary use

In many buildings, such as hospitals, substations, TV and radio stations or industrial plants inpatient units are used, which have to start up reliably. The ramp-up of the aggregates under load is not possible. Therefore, a battery-backed uninterruptible power supply is necessary to compensate for short outages, to allow starting up the group (if the battery runs low ), and to feed the possibly prescribed emergency lighting. In addition to investments arising running costs for maintenance and regular test runs, where no failure of the public network has occurred.

Another example is the field of logistics. Here is a part of the data processing is powered by stationary equipment, for example, to ensure access to the ERP system during a power failure.

Mobile use

There are also smaller, mobile devices that are portable or can be mounted on trailers. These are widely used in civil protection as in the fire service. They are used not only in case of power failure, but also in areas without power supply, for example, for water treatment systems of KHDS, the THWs or other organization. The units, which are used by the civil protection have in the small, usually portable versions power from 2.5 to 14 kVA. These are usually aggregates that have multiple 230 -volt grounded outlets and are also usually still equipped with a three-phase connection. The modern equipment of THWs be powered with four- stroke engines. However, there are still older models to find with two-stroke engines drive. However, these are increasingly being used instead because of their unreliable starting. Will they still continue to be used, then for the reason that the engine works better than a 4 - stroke engine under certain conditions. Aggregates of the emergency services are usually synchronous generators that can guarantee (for example, an angle grinder ) the high starting currents of the necessary equipment. The trailer -mounted units are mostly equipped with diesel engines, which provide a service in the range 20-630 kVA.

Board power supply

Also mobile units are used for the on-board power supply of aircraft during servicing or before the start. If the aircraft are powered from the mains power to come because of the different voltage (110 volts ) and frequency ( 400 Hz) frequency used.

Scooters

In the electric vehicle sector generating sets are used for range extension, see Range Extender.

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