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three-phase HV / LV transformers mineral oil-immersed distribution models
Instructions for installation, commissioning and maintenance Contents taking delivery
HV and LV connections
transformer operation in parallel
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Warning This guide intended for standard range oil-immersed distribution transformers as described in France Transfo product catalogues. If in doubt, our After-Sales Service remains wholly at your disposal. Tél. (33) 03 87 70 57 72 fax: (33) 03 87 70 56 21
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Taking delivery of equipment and preliminary checking On receipt of equipment, ensure that it corresponds with your order by checking machine characteristics indicated on the rating plate (capacity, voltages, etc.) Distribution transformers are delivered "ready for installation", i.e. completely filled with oil and with accessories either fitted or delivered separately. When unloading, check that the transformer has not been damaged during transport (broken insulators, damaged tank, etc.) and that all accessories ordered have been delivered. Also check that the tank lead seal, fixed to one of the cover screws (usually at a tank corner) is intact, because its breakage causes the transformer guarantee to lapse. Should the unit have been damaged or if accessories ordered are found to be missing: m
enter a reservation on the final haulage contractor's delivery note and confirm by recorded delivery letter within 3 days.
write a report and send it immediately to your supplier (France Transfo or a dealer as the case may be).
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Handling Transformers are usually stabilised during transit by heavy timber bearers fixed to the vehicle bed. It is therefore essential to remove these bearers before lifting the transformer unit off the vehicle.
Transformer units incorporate specific handling devices. m
Lifting by means of slings or a lifting beam (figure 1)
The unit must be handled using the 2 lifting rings located on the transformer cover. m
Hauling (figure 2)
The transformer must only be hauled from its chassis. 30 mm diameter holes have been drilled in the ends of chassis members for this purpose, except in the case of low capacity units or those built to a special specification. Hauling must only been undertaken in two directions: along and perpendicular to the chassis centreline. m
Handling using a forklift truck (figure 2)
Forks must only lift the chassis from within the inverted channel sections, with idler rollers removed.
2 hole for hauling
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Positioning of idler rollers (figure 3)
either by lifting with slings or a lifting beam.
or by lifting with a forklift truck. In this case, position the forks of the truck within the inverted channel sections. Place heavy timber bearers, which are slightly higher than the idler rollers, crosswise beneath the ends of the chassis members and lower the unit onto these timbers. Position jacks and remove timber bearers one by one. At the same time, fix each idler roller in the required position (idlers swivel in 2 directions) using the locking screw. Then, remove the jacks and allow the unit to rest on its idler rollers. Ground clearance due to the idler rollers is essential for transformer cooling.
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Installation Ensure that machine characteristics shown on the rating plate correspond with installation conditions: primary voltage(s), tapping links. This plate may be moved and attached to any side of the tank so that it is visible once the machine is in position. In general, installation must comply with the requirements of IEC Standard 71-1, 2 and 3 in relation to insulation co-ordination. E.g.: case of overhead-underground connection to be protected by lightning arresters installed at both ends of the HV cable. m
unit to be installed at a maximum altitude of 1000 m, unless otherwise specified with order, because air rarefaction adversely affects cooling of the windings.
unless otherwise specified with order, transformers of standard design are sized in accordance with IEC Standard 76 for the following ambient temperatures: • maximum • average daily • average annual • minimum
: 40°C : 30°C : 20°C : – 25°C
When the transformer is live, the ambient temperature inside the plantroom must comply with the above values, unless the transformer has been specially designed on the basis of a particular specification.
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Installation Determining the height and cross-sectional areas of ventilation wall openings (figure 4)
In the general case involving natural cooling (AN), the purpose of the plantroom ventilation system is to disperse the heat, resulting from the total heat losses generated by the operating transformer, by natural convection.
S’ 200 mm mini
An efficient ventilation system comprises a fresh air inlet wall opening of crosssectional area S positioned low down in the room, and air outlet opening of crosssectional area S' positioned high up on the opposite wall of the room at a height H above the air inlet opening. It should be noted that restricted air circulation around the unit causes a reduction in available power. For this reason, the transformer must be positioned at a minimum distance of 200 mm from any solid wall.
H Groupe Merlin Gerin · Usine de Maizières-lès-Metz (Moselle) France
Design calculation: P = sum of losses under no load and losses due to load on transformer, expressed in kW at 75°C, plus losses generated by any other unit in the same room. S = cross-sectional area of fresh air inlet wall opening (deduct possible area obstructed by grill), expressed in m2. S’= cross-sectional area of air outlet wall opening (deduct possible area obstructed by grill), expressed in m2. H = difference in height between inlet and outlet wall opening centre-lines, expressed in m. 0, 18P S = ----------------- and S′ = 1, 10 × S H
This formula is valid for an average annual ambient temperature of 20°C and at a maximum altitude of 1000 metres. France Transfo
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Installation Forced ventilation of plantroom (figure 5)
A ventilation system of this type is required for a cramped or poorly ventilated plantroom, or for a room in which the ambient temperature is much higher than the temperature outside, in view of the ambient temperatures used for designing the transformer. Should the transformer be frequently overloaded, a forced ventilation system can help to disperse the heat generated by the unit, although it will not reduce the adverse effects of such overloading on the equipment's life.
S’ 200 mm mini
An air extract fan discharging outside the plantroom may be fitted to the outlet wall opening, located at high level, in order to increase natural convection in the room; this fan can be thermostat-controlled. Recommended discharge rate (m3/s) at 20°C = 0.10 P P = total heat losses to be dispersed, expressed in kW, for all equipment installed.
Groupe Merlin Gerin · Usine de Maizières-lès-Metz (Moselle) France
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Installation Setting the voltage commutator Adjustments to tapping point or voltage commutators must be undertaken with the transformer off-load and de-energized.
©Tapping links Set the tapping point commutator to the required position: Pos. 1: upper primary voltage Pos. 2: rated primary voltage Pos. 3: lower primary voltage red locking knob
- unscrew fully the red locking knob, - simultaneously pull and turn the commutator rotating head until the pointer indicates the right setting, - push the rotating head back ensuring that the pointer is engaged in the notch for the setting required, - rescrew fully the red locking knob
commutator rotating head
©Double primary voltage For units using 2 primary voltages, select position as required.
Commutator setting is carried out in the following way:
Pos. 1: HV1 Pos. 2: HV2
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Installation Statutory restrictions for oil-immersed transformers Each country issues its own regulations covering the installation of oil-immersed transformers on its territory. These regulations invariably respond to concerns for the protection of people, property and the environment. Available protection systems depend on the technology adopted for the transformer concerned. When the unit is in service, the volume of the dielectric fluid used to cool its coils (usually mineral oil complying with IEC Standard 296) varies continually, due to temperature variations in the windings. These volume changes must be "absorbed" by a suitable expansion system which has given rise to two distinct technologies:
Hermetically sealed type transformer The unit's tank, containing the active part, is hermetically sealed: variations in volume are absorbed by expansion of the cooling fins positioned around the tank, the dielectric fluid is not exposed to the surrounding air. Maintenance of this type of unit is thus greatly reduced (see page 20).
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Installation Protection accessory: the protection relay (figure 6)
Fitted directly to the transformer cover, this relay ensures protection against internal faults, prolonged overvoltages and fire risks associated with the use of inflammable dielectric fluids. The accessory continuously monitors: - dielectric fluid level, - tank internal pressure, - dielectric fluid temperature at two different thresholds.
To operate properly, the protection relay must be fully filled with fluid (level higher than the float visible in the transparent section of the unit). If this is not the case, check the instructions which appear inside each casing.
To ensure optimum protection, the following action and adjustments are recommended: Finding
Action to be taken
Gas emitted or drop in level
Large float at the top
➩ Serious fault
➩ De-energize unit
➩ Serious fault
➩ De-energize unit
Thermostat threshold 1
➩ Activate alarm
Thermostat threshold 2
➩ De-energize unit
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Installation Faults detected on live transformer unit m
Dielectric fluid level is detected as low The protection relay is empty and the large float is at the bottom. May be due to: - air entering; there must be a dielectric fluid leak and thus oily stains should be visible on the ground. Accurately localise the fault, carry out repair, then recheck the level with the body of fluid at a temperature of 20°C, before switching the unit live again (see oil grades, page 20), - internal gas emission: gas should be sampled using a syringe and then analysed. Whilst awaiting results, under no circumstances should the transformer be switched live again because a risk of total destruction exists. Should gas analysis reveal an inflammable gas, contact FRANCE TRANSFO After-Sales Service (see page 23), or your SCHNEIDER correspondent.
Overheating is detected This may be due to: - improper cooling of the transformer (insufficient air flow around unit or plantroom ventilation), - continuous overvoltage.
Excess pressure is detected This may be due to: - overheating: see above, - internal gas emission: see above, - topping up of dielectric fluid with the body of fluid below 20°C; drain the overflow with the transformer de-energised and the dielectric fluid at 20°C.
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Installation Breather type transformer with expansion tank (figure 7) The transformer tank is connected by pipework to an expansion tank, mounted above the unit, which ensures that the dielectric fluid level remains sufficiently high in the transformer tank: variations in dielectric fluid volume are absorbed by the expansion tank which remains at atmospheric pressure.
This type of unit therefore requires maintenance which is both regular and suited to the climatic conditions in the vicinity of the transformer (see page 21). Protection accessory : the Buchholz relay Fitted to the pipework linking the expansion tank to the transformer tank, this accessory ensures protection against internal faults only, by monitoring dielectric fluid levels and fluctuations. To ensure proper operation, the Buchholz relay must be completely bled of air. Faults detected on live transformer unit m
Dielectric fluid level is detected as low. The Buchholz relay is partially empty, the top level float is at the bottom. Reasons for this low fluid level are the same as those given for the protection relay (see page 11) but in the present case, the relay will activate automatically the alarm.
Major discharge of oil towards the expansion tank is detected A violent emission of gas, resulting in serious electrical faults within the transformer tank, leads to a large discharge of oil to the expansion tank, which causes the Buchholz relay bottom float to pivot; the transformer unit must be de-energised immediately and permanently. Contact FRANCE TRANSFO After-Sales Service (see page 23), or your SCHNEIDER correspondent. France Transfo
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Installation Dielectric fluid retention system In an environmental protection context, the retention system used must be capable of containing the total quantity of dielectric fluid, unless otherwise specified by local regulations. It may comprise: - a raised door threshold if the plantroom floor is oil tight, - a low oil tight wall around the transformer, - a steel trough positioned beneath the transformer. In the last two cases, ensure that the system does not adversely affect transformer cooling by preventing air circulation around the tank cooling fins.
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HV and LV connections Bushing type Transformers may be provided with the following connections. LV connections to busbar bushings (only used above 250 kVA units) 100
Ø 14,5 Ø 11
35 50 50
31,5 Ø 11
HV connections to plug-in bushings
with draw-out angle connector
LV connections to porcelain bushings (mandatory for 100 and 160 kVA units) DIN 42530
with draw-out straight connector
HV connections to porcelain bushings DIN 42531 150
M 12 50
15 10 M 20 M 12
26 M 30
60 Ø 14
100 Ø 14
50 M 42
DT 250A DT 630A
N.B.: under no circumstances should porcelain HV bushings be used with cover-protected HV systems.
Example of bushing choice for LV = 400 V. kVA
LV busbar bushings
LV porcelain bushings
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HV and LV connections Assembly and tightening torque Bushings must not be subjected to stresses resulting from cable or busbar connections; such loads can cause leaks at various joints. Furthermore, the following connection details and tightening torque values shall be complied with: HV or LV connection to porcelain bushing (U ≤ 52 kV - M12 stud) nut tightening torque: 25 Nm
LV connection to busbar bushing M12 brass stud
load in accordance with I.E.C. 137: connecting terminal inclined < 30°, F = 50 daN connecting terminal inclined > 30°, F = 30 daN
clearance: approx. 5 mm
large diameter metric series steel plain washers tin-plated copper busbar bushing
reminder: 1 N.m = 0.102 mkg 1 mkg = 0.98 daN.m
N.B.: end lug, bolt and washers are not supplied.
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HV and LV connections Table of tightening torque values
M8 M10 M12 M14 M16
Class 6.8 anticorrosion -treated steel 15.2 30 52 83 130
Class A2-70 and A4-70 stainless steel 15.5 30 53 85 133
Class A2-80 and A4-80 stainless steel 17.7 35 60 97 152
7.6 15.1 25 41 55
Tightening torque given in N.m. Tightening tolerance ± 20%. The above torque values are for assemblies incorporating plain washers. However, we recommend the incorporation of contact washers behind the plain washers; the above torque values should be increased by 35% if this is done. Steel and stainless steel bolts shall be greased prior to fitting. If aluminium bolts are used, please refer to manufacturer's recommendations.
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HV and LV connections Protection HV bushings m
Draw-out connectors (straight or angle) may be kept plugged into the plug-in bushings using a padlockable locking device (padlock / lock not supplied); Release of this locking system may be made conditional on prior isolation of the transformer from the HV supply (figure 8);
Porcelain bushings may be fitted with a sealable protective cover, whose design will depend on the HV voltages, the configuration and number of cables.
LV bushings m
Busbar or porcelain bushings may be protected by a sealable cover.
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Transformer operation in parallel Connection of several transformers in parallel leads to the following constraints: m
If their power outputs are different, the total available combined power output will be slightly less (< 10%) than the sum of the power outputs for each transformer coupled separately.
The power output of the largest transformer should not be more than twice that of the smallest unit.
Transformers must be supplied by the same network.
Connections must be of the same length and have similar characteristics between the LV terminals of the different units and the coupling circuit-breaker (figure 9).
Couplings must be identical.
Short-circuit voltages must be identical (±10%).
Differences in secondary voltages between the different units must not exceed 0.4%.
The switch shall be positioned identically on each unit.
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Maintenance Mineral oil and component materials The transformer is filled with mineral oil complying with ICE Standard 296. Transformer component materials are free of polychlorobiphenyls (PCB's), polychloroterphenyls (PCT's) and polychlorobenzyltoluene (PCBT). Moreover, the PCB content of this unit is guaranteed to be less than the detectable threshold (2 ppm*) in strict compliance with standards currently in force. Hermetically sealed type transformer Under normal operating and environmental conditions, maintenance of this transformer is reduced. It is in fact limited to regularly checking the tightness of connections and visual inspection of transformer oil tightness. Under conditions of extreme pollution (depositing of dust, salt, chemicals, etc.), cleaning of porcelain or busbar bushings may be required. As long as the dielectric fluid has not been exposed to the air for a particular reason (tank opening, repairs, fitting of accessories, topping up of oil, etc.), one dielectric withstand test, on a sample taken from the bottom of the tank (minimum breakdown voltage 30 kV), every 10 years is sufficient. The transformer is hermetically sealed and has no gas cushion. In other words, filling and closure have been carried out in such a way that pressures are balanced (internal and external atmospheric pressure) under conditions approaching normal, i.e. temperature of 20°C and pressure of 1013 mbar.
* parts per million.
c des sé ave ti réali élément de n ra a g st ut ateur e xempts de to ué par e nsform té poll Ce tra nts neufs et le d’avoir é a b constitu tion suscepti ra been récupé . B r has sforme totally free des PC n a tr is is that th material and PCB’s. w h arrant We w tured with ne s polluted wit c rt manufa ond hand pa ers c nsform from se n all tra e c la d o p l e b a L
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Maintenance If necessary, this transformer may be opened in accordance with the following recommendations: m Transformer is hot (θ > 20°C) The unit's internal pressure is higher than atmospheric and opening it causes leakage of some dielectric fluid which can only be reinjected in full, once its temperature has returned to 20°C. Until this occurs, the unit can fulfil its functions. However, replacement of all the dielectric fluid lost at the earliest opportunity is preferable. m Transformer is cold (θ < 20°C) The unit's internal pressure is lower than atmospheric and opening it causes a drop in oil level in the tank. After servicing and topping up dielectric fluid, if required, put the unit back into operation and purge when hot. To prevent excess pressure in the tank, the volume of dielectric fluid which may have been added (during topping up) should be drained, once the unit's operating temperature has risen to 20°C.
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Maintenance Breather type transformer with expansion tank Because the dielectric fluid is exposed permanently to the surrounding air, the frequency of oil quality checks must be increased: once a year is an absolute minimum, which should be further increased if a gradual deterioration of fluid dielectric withstand is observed (reminder: minimum breakdown voltage: 30 kV). If an air dehumidifier has been fitted to the expansion tank to filter the incoming air, the colour of the silica gel it contains should be monitored: - blue colour : silica gel is in a good condition for ensuring dehumidification, - pink or white colour : silica gel has absorbed humidity and has become ineffective, it should therefore be replaced (supplied by our After-Sales Service, see page 23). Also check that the glass, located at the bottom of the dehumidifier, is filled with oil to the required level, in order that dust carried by the surrounding air flow is effectively retained.
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After-Sales Service When making enquiries or ordering spare parts, it is essential to quote the main characteristics given on the rating plate and, in particular, the unit serial number.
TECHNICAL MEMO (data to be copied from unit rating plate)
kVA impedance voltage
primary in service on
low voltage V V V V V A
Rated high voltage
Mass of dielectric
insulation level KV
high voltage pos 1 pos 2 pos 3 pos 4 pos 5 currents
nature windings cooling
dielectric mass diel. mass total
NAL - 226489
Groupe Schneider · Usine de Maizières-lès-Metz (Moselle) France
After-Sales Service tel.: (33) 03 87 70 57 72 fax: (33) 03 87 70 56 21
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Precommissioning checks Operations prior to connecting transformer □ check data given on rating plate in relation to needs (power output, voltage, etc...)
□ ensure transformer plantroom is clean and cannot flood □ ensure correct ventilation - plantroom air vents are clear and of suitable area (pages 7 and 8) - sufficient clearance between unit and solid walls in plantroom (page 7) - sufficient clearance between unit and floor (unit resting on idler rollers page 5)
□ check general condition and cleanliness of transformer □ measure values of insulation resistance using a 2,500 V insulation tester Measuring points
Usual values for mineral oil
HV / earth
LV / earth
If the measured values are significantly less than the usual values, please call your After-Sales Service (page 22).
□ check oil tightness of unit (welds, gaskets, valves, drains, plugs). Checks carried out on: ......................................... by: .........................................
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Precommissioning checks Operations prior to switching transformer live □ ensure there is no foreign body on the unit (metal filings, nuts and bolts, etc.) □ if the transformer is an hermetically sealed type unit fitted with a protection relay, check that the large float is at the top and that the drain is properly closed (close by turning clockwise). Refer to instructions supplied with each transformer in relation to testing.
□ if the transformer is a breather type unit with an expansion tank and Buchholz relay, check that all air bubbles have been bled from the latter unit and carry out relay testing using the devices provided for this (rod to be pushed or pulled to activate alarm or trip). Check condition of silica gel in the dehumidifier and the level of oil in the bottom glass vessel.
□ ensure that cables and busbars are properly supported; no loads should be applied to the transformer connection lugs.
□ check wiring of protection or ventilation auxiliaries with respect to: - insulation clearances and cable fixings,
□ operation.check tightness of connections (pages 16 and 17) □ check earthing continuity - to ensure the safety of operating personnel, the transformer earthing system must be grounded.
□ check that rotating switch head is correctly set to, and locked in, the required position.
□ ensure that ventilation grills are clear. - if unit is to operate in parallel, check short-circuit voltage, phase consistency and voltage ratio (page 19)
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France Transfo BP 10140 F 57281 Maizières-lès-Metz Cedex Tel.: (33) 03 87 70 57 57 fax.: (33) 03 87 51 10 16
Since this manual was edited, a number of alterations may have been incorporated in the equipment you have received. The sole reason for this resides in our constant efforts to improve the quality and performance of our equipment.
GEa 220000 a
Edited by: France Transfo - 03/99 Typesetting and illustrations: COREDIT
N° ident. TVA : FR 78 357801109 • SA au capital de 10 280 000 FRF – RCS Metz B 357 801 109 • Imprimé en France
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