First 600 kV AC Dry Type Current Transformers Put Into Service in North America

600 kV Dry Type Transformers Energized in the MMTP Transmission Project

On June 1, 2020 the first ever 600 kV AC dry type current transformers installed in North America were energized and put into service in the Province of Manitoba, Canada. Manitoba Hydro, the publicly-owned electric and natural gas utility for the Province of Manitoba purchased six (6) RHM International 600 kV dry type LRGBJ-ZH-600 current transformers for the Manitoba – Minnesota Transmission Project (MMTP) which involved the building of a 500 kV AC transmission line from the City of Winnipeg area to the United States of America border, then continued as the Great Northern Transmission Line to the Iron Range 500 kV AC Substation near Grand Rapids, Minnesota, USA. The 600 kV dry type current transformers purchased for the new MMTP 500 kV AC line’s protection and metering requirements were installed at Manitoba Hydro’s Dorsey and Riel Converter Stations.

Technical Specifications for the 600 kV AC Dry Type LRGBJ-ZH-600 Current Transformers Supplied for the Manitoba-Minnesota Transmission Project (MMTP)

MMTP Transmission Line Facilitates Manitoba Hydro Export Sales to US

This was a very important project for the utility as it allowed Manitoba Hydro to fulfill their export sales agreements while providing increased access to new markets in the USA for future sales. Export sales are an important revenue source for the utility as it allows Manitoba Hydro to have domestic electricity rates among the most competitive in North America.

LRGBJ-ZH-600 Dry Type Current Transformer

The LRGBJ-ZH-600 dry type current transformer is a cascade double decker two stage design, composed of two CTs (an upper CT unit and lower CT unit) each with a rated voltage of about 300 kV. The pedestal of the upper CT unit is bolted to the top of the lower CT unit. In this configuration the secondary of the upper CT unit is electrically connected in series with the primary winding of the lower CT unit. The cascade design also allows the LRGBJ-ZH-600 current transformer to be shipped in two separate CT pieces which makes it easier to transport and install at site.

Dry Type CTs Have Better Safety Profile

The RHM International dry type CT design has eliminated the safety risks and maintenance issues associated with the use of oil, kraft paper, pressurized insulating gas, and the porcelain insulator bushing. The RHM International dry type CT has been designed for a minimum life expectancy of forty (40) years, with additional decades of trouble-free operation expected.

“We should be excited about the advent of new technologies that support the environment and promote safety and reliability.”
-- Derek Barker, P.Eng., Apparatus Quality Control, Manitoba Hydro

Technical Specifications for the 600 kV AC Dry Type LRGBJ-ZH-600 Current Transformers Supplied for the Manitoba-Minnesota Transmission Project (MMTP)

Nominal system voltage	500 kVrms
Maximum continuous operating voltage	600 kVrms
Rated primary current of upper CT unit	2000 x 4000 A
Rated primary current of lower CT unit	16 A
Primary current rating factor	1.0
Rated secondary current of upper CT unit	16 A
Rated secondary current of lower CT unit	5-5-5-5 A
Secondary current rating factor	1.0
Accuracy class and burden (on maximum taps)	10L800 and 0.3B1.8 at 0.9 PF
Protective class	PX. Ratings: Vk ≥ 800V, Iexc ≤ 10A
Number of primary sections	2
Number of cores	4
Rated power frequency 1 minute withstand	860 kVrms
Rated lightning full wave impulse withstand	1800 kVpeak
Rated lightning chopped wave withstand Rated switching impulse withstand	2070 kVpeak 1300 kVpeak
1 sec thermal short circuit fault rating	63 kArms
Mechanical dynamic short circuit rating	150 kApeak
Ambient temperature operating range	-50°C to +40°C
Creepage distance (heavy pollution, 25mm/kV)	15000 mm
Seismic level	High
Capacitance tap	Full 100%
Internal arc protection	Class II
Design life expectancy (minimum)	40 years
Measurement Canada approval no.	AE-2354

REFERENCES
1) Manitoba–Minnesota Transmission Project. MMTP Project Description

2) Great Northern Transmission Line.