- #1
RAHMAN
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cable size calculation
between QRM and 11kv to 400v transformer (1500 kva)
between QRM and 11kv to 400v transformer (1500 kva)
How to calculate the cable size between QRM and transformer
- Thread starter RAHMAN
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- Cable Transformer
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Discussion Overview
The discussion revolves around the calculation of cable size between a Quadrilateral Ring Main Unit (QRM) and an 11kV to 400V transformer with a capacity of 1500 kVA. Participants explore various factors influencing cable sizing, including material type, installation conditions, and short-circuit ratings.
Discussion Character
- Technical explanation
- Debate/contested
- Homework-related
Main Points Raised
- One participant requests more context and specific questions to facilitate a meaningful response.
- Another participant questions the meaning of QRM and inquires about the cable material, installation conditions, and insulation temperature ratings.
- A participant clarifies that QRM refers to a Quadrilateral Ring Main Unit and explains the types of Ring Main Units (RMUs) used for redundancy of feeders.
- A formula for calculating the cable cross-sectional area based on short-circuit current is provided, including specific parameters such as initial and final conductor temperatures.
- Another participant expresses appreciation for the technical response regarding the use of NEC Table 240.92(B) for determining cable ratings.
Areas of Agreement / Disagreement
Participants generally agree on the need for specific information to accurately calculate cable size, but there is no consensus on the initial question due to varying interpretations of QRM and the lack of detailed context from the original poster.
Contextual Notes
Limitations include the need for additional details about the installation conditions, cable material, and specific parameters for calculations, which are not fully provided by the original poster.
Who May Find This Useful
This discussion may be useful for electrical engineering students or professionals involved in cable sizing and transformer connections, particularly those interested in practical applications of electrical codes and standards.
- #2
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I see this is your first post. You have to provide more context and be more specific in your questions before we can answer. You asked no question at all.
If you are a student and this is a homework assignment, you must use a homework forum.
https://www.physicsforums.com/forums/engineering-and-computer-science-homework.158/
- #3
jim hardy
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What's a QRM?Is your cable copper or aluminum, is it run in air or in conduit, and if buried what is thermal conductivity of Earth covering it?
What is temperature rating of your insulation ?
That's why we have electrical codes, so that one avoids 'beginner's mistakes' .
What is temperature rating of your insulation ?
That's why we have electrical codes, so that one avoids 'beginner's mistakes' .
- #4
Babadag
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QRM has many meanings, I agree with you Jim. Anyway, in my opinion, the o.p. is
referring to Quadrilateral Ring Main Unit. RMU (Ring Main Unit) is of two types. TRM (Triangular Ring Main Unit) & QRM (Quadrilateral Ring Main Unit). TRM is (2 Feeder+ 1 Transformer Feeder) and QRM is (2 Feeder + 2 Transformer Feeder). RMU is mainly used for redundancy of feeders.
So, a sketch it could explain more.
The short-circuit current will state the cable cross-section area. If you know the circuit breaker short-circuit rated current then you may use the NEC Table 240.92(B) Tap Conductor Short-Circuit Current Ratings.[for copper conductor]:
A=I/SQRT(0.0297*LOG10((T2+234)/(T1+234))/t) where:
I = short-circuit current in amperes
A = conductor area in circular mils
t = time of short circuit in seconds (for times less than or equal to 10 seconds)
T1 = initial conductor temperature in degrees Celsius.
T2 = final conductor temperature in degrees Celsius.
T1=75oC usually T2=250oC for XLPE or EPR conductor insulation.
Let's say I=20000 A T2=250oC t=1 sec T1=75oC then A= A=26300 cmls [=135 mm^2].
referring to Quadrilateral Ring Main Unit. RMU (Ring Main Unit) is of two types. TRM (Triangular Ring Main Unit) & QRM (Quadrilateral Ring Main Unit). TRM is (2 Feeder+ 1 Transformer Feeder) and QRM is (2 Feeder + 2 Transformer Feeder). RMU is mainly used for redundancy of feeders.
So, a sketch it could explain more.
The short-circuit current will state the cable cross-section area. If you know the circuit breaker short-circuit rated current then you may use the NEC Table 240.92(B) Tap Conductor Short-Circuit Current Ratings.[for copper conductor]:
A=I/SQRT(0.0297*LOG10((T2+234)/(T1+234))/t) where:
I = short-circuit current in amperes
A = conductor area in circular mils
t = time of short circuit in seconds (for times less than or equal to 10 seconds)
T1 = initial conductor temperature in degrees Celsius.
T2 = final conductor temperature in degrees Celsius.
T1=75oC usually T2=250oC for XLPE or EPR conductor insulation.
Let's say I=20000 A T2=250oC t=1 sec T1=75oC then A= A=26300 cmls [=135 mm^2].
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- #5
jim hardy
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Babadag said:
What an excellent answer !
- #6
Babadag
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Thank you Jim.
Thank you very much indeed !
Thank you very much indeed !
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