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Transformer Room Design

Transformer Room Design IEC 61936-1 

Essential spatial requirements are described in IEC 61936-1  (VDE 0101-1). The propagation of fires, the noise level, ventilation, water pollution, and protection against indirect contact must be taken into account. Furthermore, the  standard refers to the relevant national, regional, and local  provisions and regulations. In addition, product-specific  characteristics as described in the IEC 60076 (VDE 0532-76) series of standards play a role for room planning.

Conditions for installation and room layout

Extreme local conditions must be taken into account when  planning the system:

• The paint finish and prevailing temperatures are relevant for use in tropical climates

• For use in altitudes of more than 1,000 m above sea level a special configuration with regard to heating and insulation level is required, see IEC 60076-11 (VDE 0532-76-11)

• With increased mechanical demands being made use in a ship, excavator, earthquake region, etc. additional constructive measures may be required, e.g. supporting the upper yoke

Cast-resin transformers can be installed in the same room as medium- and low-voltage switchgear with-out any extra precautions . This helps save considerable costs for transformer cells. In contrast to a room for oil-immersed transformers, this room can be provided at 4m below ground surface or at the top floor of buildings.

With regard to fire protection of facilities, national or local regulations must usually be observed. For example, in Germany the EltBauVO (Ordinance on the construction of 
electrical operating areas) governs that doors in fire resistance class F30-A separate the electrical operating room (in accordance with DIN 4102-2) and walls in fire resistance 
class F90-A. However, firewalls (24 cm wall thickness) as for oil-immersed transformers, are not required for cast resin  transformers.

The EltBauVO also governs that the spatial separation towards other rooms must not be endangered as a result of a pressure surge due to an arcing fault. In terms of ventilation, it must also be observed that electrical operating areas must be directly vented into open air or by using separate intake / discharge air pipes. Air pipes leading through other rooms must designed in a fire-resistant manner and the openings into open air must have protection grilles. Oil-immersed transformers (using mineral oil or synthetic fluids with a fire point ≤ 300 °C) require at least one exit leading directly outdoors into open air, or through 
an ante-room (without any connection to other rooms, except for the switchgear room if applicable).

Transformer Room Layout

The transformers are suitable for operation up to an altitude of 1,000 m above sea level. When installed in altitudes higher than 1,000 m, special versions are required. For every 100 metres that the permitted altitude of installation is exceeded, the nominal power must be reduced by approximately 0.4 % for liquid-filled transformers, and by approximately 0.5 % for cast-resin transformers.

Transformer room ventilation and pressure estimate in case of an arcing fault
Heat loss generated during any kind of transformer operation must be dissipated from the transformer room, see below figure . The possibility of natural ventilation should be  checked first. If this is not sufficient, a mechanical ventilation system must be installed.

The heat loss results from the power loss of the trans-former. The power loss of a transformer is:

Pv = P0 + 1.1 · PK120 · (SAF / SAN)2 [kW]

P0:                  No-load losses [kW]

1.1 · PK120:   Load losses at 120°C (according to the list or, if already available, the test                             certificate specifications), multiplied by a factor of 1.1 for the working 
                       temperature of the insulation categories HV / LV = F / F for GEAFOL                                        transformers.

SAF:                Apparent Power [kVA] for forced ventilation AF (air forced)

SAN:               Apparent power [kVA] for natural ventilation AN (natural air flow)

The total heat loss in the room (Qv) is the sum of the heat losses of all                             transformers in the room:

Qv = Σ Pv

Calculation of the heat dissipation

The following methods are available for the dissipation of the entire power loss Qv in the room:

Qv1 dissipation with the natural air flow

Qv2 dissipation via walls and ceilings

Qv3 dissipation with the forced air flow

Qv = Pv = Qv1 + Qv2+ Qv3

To illustrate the size of the variables for the different ventilation methods, linear dependencies can be derived by specifying realistic values. For a thermally effective height 
of 5 m, an air temperature rise of 15 °C between the inside and outside area, a uniform heat transfer coefficient of

3.4 W / m2 for 20 cm thick concrete and an air flow rate of 10,000 m3 / h for forced ventilation, which is led through an air duct with an inlet / outlet cross section that is approximately four times as large.

Qv1 = approx. 13 [kW / m2] · A1,2 [m2] 
(Example: Qv1 = 8 kW for a cross section of approx. 0.62 m2)

Qv2 = approx. 0.122 [kW / m2] · AD [m2] 
(Example: Qv2 = 8 kW for a surface area of approx. 66 m2)

Qv3 = approx. 44 [kW / m2] · A1,2 [m2] 
(Example: Qv3 = 8 kW for a cross section of approx. 0.18 m2)

These simple examples show that the heat dissipation through walls and ceilings quickly reaches the limits of the room and that for large transformer outputs, a 
detailed configuration of the forced ventilation may be necessary.

This article was extracted from "Planning of Electric Power Distribution" by Siemens

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