INTEGRATED POWER SUPPLIES
RATED POWER 1 TO 7,5 KVA, 220/240 V PROTECTION DEGREE IP20
The power supply of telephone plants and FM/TV relay stations has always entailed numerous problems and specific needs which are difficult to meet, among them:
- to assure the safety of operators working on the plants, ac-cor-ding to the law;
- to assure continuity of ope-ra-tion to the plants;
- to build a compact di-stri-bu-tion system for all loads usually present in relay stations;
- to limit the costs of in-stal-la-tion and management;
- to allow a cheap and ef-fec-tive technical assistance.
SAFETY FOR OPERATORS
The primary consideration has always been the safety of operators working on the equipment, as established in EEC directives 89/391/Eg, 89/654/Eg, 89/656/Eg, 90/269/Eg, 90/270/ Eg, 90/394/ Eg, 90/679/Eg “on the improvement of the safety and health of workers in the work place”.
The problem can be solved by producing professionally made equipment and by simply applying the International Standards HD 384/4/41, IEC 364-4-41 “Electrical installations of buildings – Part 4: Protection for safety – Chapter 41: Protection against electric shock”.
This regulation describes protective measures intended to ensure the safety from electric shock in normal service and in case of fault. It also includes particular requirements applicable to TN, TT and IT system earthing. It is considered a basic safety publication.
Chapter 41 “Protection against electric shock”
Art. 412 “Protection against electric shock in normal service (protectionagainst direct contact or basic protection)
Art. 412.1 Protection by insulation of live parts
Art. 412.2 Protection by barriers or enclosures
Art. 413 “Protection against electric shock in case of fault” (protection against indirect contact)
Art. 4184.108.40.206 Protection by automatic disconnection of supply
Art. 413.5 Protection by electrical separation
Remark: for voltage bands for electrical installations of buildings, see IEC 449. It has the status of a basic safety publication in accordance with IEC Guide 104.
CONTINUITY OF OPERATION
The continuity of operation required by an automatic repeater, often installed in practically inaccessible sites, must satisfy a variety of requirements, ranging from the prevalently technical to the economic, limiting the need for intervention on the equipment.
The first problem to arise, and probably also the most difficult to tackle, is that of protection against atmospheric discharges, practically omnipresent in repeaters on account of the sites they have to be installed in. Due to the coupling of electromagnetic fields and the conduction in cables, the effect of lightning spreads for several kilometres from the impact point.
On the other hand, other forms of protection, for example those against overloads and short circuits, are subject only to suitable dimensioning.
The use of earth leakage trips for protection against direct contacts must be ruled out as even the overcurrents of feeble intensity caused by factors such as merely even inductance can result in untimely opening of the circuit. The importance of the economic aspect lies not only in the costs of making and maintaining the equipment, but also in the question of audience return. In fact, failure to guarantee the customer full operation of the equipment constitutes an interruption of the service and, accordingly, a cost.
CONTROLS AND FUNCTIONS
The integrated power supply AI is housed in a 19” rack cabinet. It includes the following components:
a. a spark-gap magnetic blow-out lightning arrester. This is an essential component of the integrated power supply. It is characterized by:
- high precision striking voltage with any overvoltage waveform;
- restoration of the plant normal operating conditions in-ter-rup-ting the arc current at its first passage through 0 after the exhaus-tion of the overvoltage wave;
- capability of withstanding currents with peak value of 100 kA (10/350 µs), charge of 80 As and specific energy of 1,25 MJ/Ω;
- auto-regenerability. Thanks to this characteristic, the arrester does not need to be replaced, as it happens with other over vol-ta-ge protec-tion systems.
b. An input circuit breaker, providing protection against short circuits and acting as main circuit breaker. It has a high ma-gne-tic tripping characteristic, avoiding untimely openings following im-pulse type overcurrents caused by atmospheric discharges.
c. A single-phase isolation transformer compliant with EN60742 Standard, provided with electrostatic shield between the windings. In addition to the galvanic isolation of the users from the line, it also ensures good attenuation against common and transverse mode conducted noise. On the secondary of the isolation transformer there are four lines, each one protected by a suitably rated circuit breaker, used for the power supply of a receiver (RX), a transmitter (TX), auxiliary equipment (e.g. air conditioner) and users (welder, drill). There is a multi-standard socket on each output. The breakers are fixed on a fiberglass support with high mechanical resistance in order to assure an adequate isolation from the metal frame.
d. A device signalling breakdown of insulation with relevant contact wired to the terminal board. This device intervenes when the insulation is lower than 100kΩ.tramite contatto riportato a morsettiera. Esso interviene quando l’isolamento è inferiore a 100 kΩ.