Design for Grounding of a Balanced TCT Type Transformer

Grounding of a balanced TCT type transformer located in a production building

Task:

Facility: Grounding of a balanced TCT type transformer located in a production building.
Soil at the site: sand clay.
Soil resistivity: 100 Ohm/m.
According to item 1.7.101 of the EIC, the resistance of the grounding arrangement to which neutral wires of generators or transformers of single-phase current source terminals are attached, in any season of the year, should be not more than 2, 4, or 8 Ohm, respectively, with the linear voltage 660, 380, and 220 V of a three-phase current source.
In this option, the linear voltage is 380 V; therefore, the resistance of the grounding arrangement should not be more than 4 Ohm.

Solution:

The grounding arrangement consists of three vertical electrodes (copper-plated threaded rods D14; 1.5 m ZZ-001-065 - 2 pcs per 1 electrode), which are interconnected by a copper-plated bar 30 x 4 GL-11074 laid in a trench at least 0.5 m deep from the ground surface and attached to the "ground" terminal of the transformer using a copper-plated bar 30 x 4 GL-11075.

Calculation of resistance of the grounding arrangement:

Vertical electrode (single) resistance:

where:
ρ = 100 Ohm·m is soil resistivity;
L = 6 m is vertical electrode length;
d = 0.014 m is vertical electrode diameter;
T is deepening, i.e. the distance from the ground surface to the grounding arrangement, m:

Calculation of resistance of a grounding arrangement for a balanced TCT type transformer

Ом - Ohm

where t = 0.5 m is the electrode top deepening.

Calculation of resistance of a grounding arrangement for a balanced TCT type transformer

м - m

Horizontal electrode resistance:

Calculation of resistance of a grounding arrangement for a balanced TCT type transformer

Ом - Ohm

where:
ρ = 100 Ohm·m is soil resistivity;
b = 0.03 m is horizontal electrode bar width;
h = 0.5 m is horizontal electrode depth;
L_гор = 20 m is a total length of the horizontal electrode.

Calculation of resistance of a grounding arrangement for a balanced TCT type transformer

Ом - Ohm

Electrical impedance of the grounding arrangement:

where:
n is set amount;
k_util hr = 0.75 is utilization ratio.

Calculated resistance of the grounding arrangement is 3.47 Ohm, which is less than the required value of 4 Ohm.

List of required materials:

№	Image	Part number	Name	Amount	Unit weight, kg
1		ZZ-001-065	ZANDZ Copper-plated threaded grounding rod (D14; 1,5 m)	20	1,9
2		ZZ-002-061	ZANDZ Threaded coupling	16	0,08
3		ZZ-002-061	ZANDZ Termination	5	0,07
4		ZZ-004-060	ZANDZ Guide head for jackhammer attachment	4	0,09
5		ZZ-005-064	ZANDZ Conductor connection terminal (up to 40 mm)	5	0,31
6		ZZ-006-000	ZANDZ Conductive grease	2	0,19
7		ZZ-007-030	ZANDZ Waterproofing tape	2	0,442
8		ZZ-008-000	ZANDZ Attachment to the hammer (SDS max)	1	0,48
9		GL-11404	GALMAR Inspection pit	5	2,6
10		GL-11075	GALMAR Copper-plated steel strip 30 х 4 mm	30 (meters)	0,98

Appendix: design in DWG and PDF formats

Согласовано - Approved by
Взам. Инв. № - Repl. Inv. No.
Подп. И дата - Sign. and date
Инв. № подл. - Orig. Inv. No.
Изм. - Rev.
Кол. Уч. - Mod. Q-ty
Лист - Sheet
№ док. - Doc. No.
Подп. - Sign.
Дата - Date
Разраб. - Developed by
ТЦ ZANDZ - ZANDZ TC
Проверил - Checked by
Н. контр. - QC
Заземление симметрирующего трансформатора - Grounding of a balanced transformer
Стадия - Stage
Лист - Sheet
Листов - Sheets
1,5 м - 1.5 m
5 м - 5 m
Зажим для подключения проводника ZANDZ ZZ-005-064 - ZANDZ Conductor connecting clamp ZZ-005-064
GALMAR Колодец контрольный GL-11404 - GALMAR Inspection well GL-11404
Сварное соединение контура заземления с заземляющим проводником - Welded connection between grounding circuit and grounding wire
Заземляющий проводник полоса омедненная 30х4 (GL-1107) - Grounding wire, copper-plated strip 30 x 4 (GL-1107)
Штырь заземления омедненный резьбовой D14, 1.5 м (ZZ-001-065) – 4 шт. - Threaded copper-plated grounding rod D14, 1.5 m (ZZ-001-065), 4 pcs
Муфта соединительная резьбовая ZANDZ ZZ-002-061 - ZANDZ Threaded coupling ZZ-002-061