Partial Discharge Test

In terms of interpretation of partial discharge measurements, the results shall be considered acceptable and no further partial discharge tests required under the following conditions:

a) The magnitude of the partial discharge level does not exceed 500 pC during the 1 h test period.

b) The increase in partial discharge levels during the 1 h period does not exceed 150 pC.

c) The partial discharge levels during the 1 h period do not exhibit any steadily rising trend, and no sudden sustained increase in the levels occurs during the last 20 min of the test.

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Reference:

IEEE C57.12.90: Test Code for Liquid-Immersed Distribution, Power, and Regulating

The Network Management System (NMS)

The Network Management System (NMS)

The Network Management System (NMS) is the supervisory control and data acquisition tool. It performs the following functions:

1- SCADA, 

2- The Real Time Network Analysis

3- The Study Network Analysis.

4- Training Simulation.

It provides the real time voltage and loading on the transmission system as well as monitoring and control of the status of the switches and breakers connecting the equipment to form the integrated network for the purpose of safe and reliable operation of the transmission system.

The NMS also provides predicative assessment tools which help in providing awareness of the situation of different elements of the electrical transmission grid to the operator. 

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Reference: Hydro One Operations Capital

Electrical Fun with Maya Angelou

Maya Angelou (1) said: 

"Talent is like electricity. WE don’t understand electricity. We use it.”

I say: 

“Talent is like electricity. Electrical engineers understand electricity. Therefore electrical engineers understand how talented they are!”

Masoud

June 21 2014

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(1) Excerpts from Dr. Maya Angelou's website on her biography:

Dr. Maya Angelou is one of the most renowned and influential voices of our time. Hailed as a global renaissance woman, Dr. Angelou is a celebrated poet, memoirist, novelist, educator, dramatist, producer, actress, historian, filmmaker, and civil rights activist.

Born on April 4th, 1928, in St. Louis, Missouri, Dr. Angelou was raised in St. Louis and Stamps, Arkansas.

Dr. Angelou has served on two presidential committees, was awarded the Presidential Medal of Arts in 2000, the Lincoln Medal in 2008, and has received 3 Grammy Awards. President Clinton requested that she compose a poem to read at his inauguration in 1993. Dr. Angelou's reading of her poem "On the Pulse of the Morning" was broadcast live around the world.

Dr. Angelou has received over 50 honorary degrees and is Reynolds Professor of American Studies at Wake Forest University.

Oil Containment Dimensions and safe distance between Power Transformers

Oil Containment Dimensions 

and 

safe distance between Power Transformers 

The effective volume of the oil containment shall be greater than or equal to the 110 per cent of the transformer oil. In case the oil containment is filled with gravel, the above percentage shall apply to the available volume of the containment (air pockets) for oil in case of an oil spillage. 

The volume of oil of a specific size transformer, might be different for different manufacturers. The BIL level can also affect the size of the tank and consequently the volume of transformer oil.

For a typical 20 MVA transformer with an Off-load tap changer,  the volume of oil  can be 5000 US Gallons or almost 19000 liters. 

Another important parameter in the design of the containment is the clearance between the transformer and containment wall. According to IEEE recommendation, the minimum horizontal distance of any oil contained part of the transformer and the containment wall would be 1.5 meters. 

Factory Mutual -the prominent insurer of industrial premises- is a good source for safty regulation and clearances and measure to mitigate the risk of hazards in heavy industrial projects including emergency generators, transformers and other station equipment.

Recommendations on the clearances of typical 20 MVA transformer would be as follows:

Between the transformer containment and a combustible wall: 25 feet (7.62 meters)

Between the transformer containment and a 2 hours fire-resistant wall: 15 feet (4.57 meters)

Between two transformers: 25 feet (7.62 meters) 

.

Note 1:  A brick wall is considered to be combustible and do not offer a 2 hours fire resistance.

Note 2: A fire wall would be required to install transformers closer to each other. Minimum distance between the transformer and the fire wall would be 1.5 meters.

Masoud Kashani

February 2014 

IESO Requirements

  

In Ontario, the protection and control as well as the communication block diagram of any new high voltage substation shall be sent to IESO (Independent Electricity System Operator) for approval. The same applies to the plans for the protection systems upgrades at existing stations.

In case the existing remote trip relays are out of date (say Statrel RT8B ), they shall be replaced with ABB NSD 570 relays and Bell S4T4 (Schedule 4 Type 4) phone circuits. Dual A and B protections for each line shall be provided to communicate with the relays at upstream Hydro One station.

The existing line impedance relay - if out of date - shall be replaced with SEL-421 relays. Reverse power protection may also be required to prevent embedded generation of feeding the grid or back feed of one line by the other in the case of distributed generation stations.

The expected in-service date for the new equipment shall be communicated to the IESO as well.

The IESO shall review the design and onfirm that the proposed upgrades will not result in a material adverse impact on the reliability of the integrated power system.

In any case, the requirements of Transmission System Code issued by Ontario Energy Board shall be satisfied.

February 14th. 2014

XLPE Cables in HDPE conduit

With regards to the material of ducts for cables the following question might arise:
Regarding the cable specification, can we specify HDPE as the material of construction for the ducts that the cable will be pulled through? Given that the temperature of the cable is rated for 90°C, will the HDPE be able to withstand this temperature?

Answer to the above questions could be as follows:
Although 90 degree C is the maximum permissible temperature at the interface of conductor/conductor shield to insulation. There are multiple heat dissipating layers which will considerably reduce the temperature when it comes to outer surface.
Bearing in mind service temperature of HDPE is 80 degree C, there might be no problem when HDPE pipe is hosting XLPE cable. On the other hand, outer jacket of cable is polyethylene (normally LDPE) and works properly while encasing the cable tightly.

Radio frequency for crane wireless remote controls

Radio frequency for crane wireless remote controls

Industrial band covers frequencies of 432-433 MHz. The radio remote controls sold by overhead crane manufacturers usually conform to international rules with regards to frequency and transmission power. Each system operates encoded and mated to its own

Should the customer require certain special frequencies then it must be sent to the manufacturer for evaluation and acceptance. However, since overhead crane manufacturers have been selling standard frequency transmitters for a long time, they are generally aware of the international and local regulations and there should not be any problem with the frequency