Metro line 4 in Budapest was implemented after dividing the project into several contractor’s contracts. One of its most complex elements covering the whole line is entitled ‘Systems and power supply’ (Tender No. Co-09). The power supply system of the metro line provides highly secure power supply for DC traction and auxiliary equipment. The 10 kV network and equipment, the whole DC traction system, the central equipment of auxiliary power supply (transformers, main distributors and uninterruptible and emergency distributors) constituted our design task.

10 kV power supply system

The first section of the metro line receives eight external power supply lines at a 10 kV voltage level from the power distribution company. In the interest of the security of supply, all metro stations with external working power supply and all back-up power supply points are supplied from a separate 120/10 kV substation of the power distribution company. Six metro stations have external 10 kV connections. These stations and the 10 kV switchgear of the Car Depot have two power supply points:one provides external power supply as specified above, and the other is joint back-up, a what is called chain cable, which runs in the metro line tunnel and is connected as a loop to these six stations and the 10 kV distributors of the Car Depot. The intermediate stations do not have external power supply. They receive delegated working and back-up power supply from two neighbouring stations (two directions) through the line tunnel. A 10 kV single-bus-bar, metal-clad switchgear was installed at every station. Its bus-bar is divided into two parts longitudinally. All switchgears contain two traction and two auxiliary branches.

DC traction network

At every metro station and car depot, a transformer station containing two traction units operates. The traction units consist of a 10/0.62/0.62 kV double secondary wound transformer provided with synthetic resin insulation and a 12-pulse silicon diode rectifier. The outlets of the rectifier are connected to a positive and negative traction distributor. Power is supplied to the single-bus-bar positive distributor through isolators, while the outlets are installed via withdrawable high speed circuit breakers. Traction power supply is of the third-rail type. The individual supply areas are separated by interruptions (air sections) established in the third rail in front of the entrance of the stations. Each area is supplied from the current converters of two neighbouring stations. In the switched-on condition of the output circuit breakers, the power supply areas are electrically connected in both directions of travel and with each other (via a positive bus-bar) in order to ensure efficient recuperation. The outlets are connected to a cable sectionalising cabinet ‘H’, using which a given station can be disconnected from the line traction network. Automatically operating short-circuiting earth switches are installed for the safe de-energisation of the third rail. The return circuits of the negative network are connected directly to the bus-bar of the metal-clad negative distributor. The negative distributor is connected to the traction units via manually operated isolators.

Auxiliary power supply system

An auxiliary power supply network was installed for the building services, electric power transmission and lighting consumers of the stations and line sections. Two auxiliary transformers were installed at every station and the Car Depot. The transformers have natural air cooling, synthetic resin insulation, a 11/0.4 kV step-down ratio, and 1,000 and 1,250 kVA power. At every station, the transformers are connected to a 0.4 kV main distributor equipped with a split bus-bar.
In normal operation, the power supply system is telemonitored.Its monitoring falls within the competence of the energy dispatcher on duty at the Dispatcher Centre in Szabó Ervin tér, Budapest.
As part of the power supply system, our Company prepared the  installation and cabling designs of the power supply equipment at Kelenföldi Railway Station, in Tétényi út, Bocskai út and Móricz Zs. körtér, and at Keleti Railway Station and the Car Depot on the basis of the system designs of the prime contractor Siemens M4 Budapest Consortium, and the as-built drawings required for technical delivery.