technical
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INNOVATION AND TECHNICAL ADVANCEMENT
Mining Circuit Protection
headoffice@cbi-electric.com.au | www.cbi-electric.com.au
Issue #05
AUG 2012
CBI | technical news
02
Mining Circuit Protection
Mining Circuit Protection
WHY CIRCUIT PROTECTION UNITS?
• Electrical distribution systems are costly
• Funds for creating these systems are limited
• Faults can sometimes be shown as low incidence
• Users may not appreciate the power and danger of electricity
• Misapplication, misuse or accidents may occur and equipment and personal safety will be at risk
• Electrical control and protection equipment reduce or eliminate these hazards
DEFINITIONS
Circuit breaker (CB)
A device with re-closable contacts capable of protecting a circuit under normal and abnormal conditions such as
overload and short circuit.
Circuit breaker rated current:
The highest current that a circuit breaker is capable of carrying continuously without tripping and without
exceeding the specified temperature level
Circuit breaker rated voltage:
The highest voltage that a circuit breaker may be used at.
Overload currents (Time Duration):
Overload currents are currents that exceed the rating of the associated cables or it’s protective device
Short Circuit (S/C) currents (Instantaneous):
Are currents of a higher magnitude than overload currents and are represented as the maximum current that can
result from a fault in a circuit
Earth leakage currents:
Currents flowing to Earth from installation live parts.
Circuit breaker rupturing capacity – kA rating:
The highest prospective current, in kilo-amps (kA) that a circuit breaker can handle at the rated voltage, under a
prescribed condition of use and behavior
Cascading
The use of circuit breakers in a series connected arrangement whereby the fully rated interrupting capacity of the
upstream breaker protects the lower rated interrupting capacity downstream breaker.
Discrimination
Discrimination is achieved only when the device directly upstream will disconnect when a fault is detected.
Discrimination is engineered into systems used for protection of over-current and short circuit situations.
CBI-electric: Australia
Free Call: 1800 770 870 | headoffice@cbi-electric.com.au | www.cbi-electric.com.au
03
CBI | technical news
Mining Circuit Protection
CHARACTERISTICS OF CIRCUIT BREAKERS
Inverse time delay: - The greater the overload,
the faster the tripping time. Contacts cannot be held in the closed position while fault persists. These protective devices
shall be suitable for the voltage and be capable of breaking any over-current up to and including the prospective shortcircuit current at the point where the device is installed.
PROTECTION AGAINST SHORT CIRCUIT
A circuit breaker shall break a current flowing in circuit conductors resulting from a short circuit in either the conductors or
the electrical apparatus supplied by the conductor system before that current can give rise to danger due to thermal and
mechanical effects produced in the conductors, connections or electrical apparatus.
Selection of the right circuit breaker shall take into account the system voltage and the prospective short-circuit current at
the place of installation.
Determination of prospective short –circuit currents may be determined by:• by an appropriate calculating method; or
• by means of a network analyzer; or
• by measurements in the installation.
General protection requirements for electrical installations for Surface mines and associated plant are laid out in
AS 3007.2 – 2004.
THE CBI ENGINEERED SOLUTION
The oldest technology that is incorporated into circuit breakers is thermal magnetic and has been used since
the first appearance of miniature and moulded case circuit breakers.
CBI uses the newer Hydraulic magnetic technology which has the following advantages:
• Offer close over current protection (typically <130% of rating – European products are rated <145%)
• Carry 100% of rated current and trip point unaffected by temperature
• Tripping mechanism not dependant on thermal application
• Tripping characteristics depend on number of coil turns and silicone oil
• No nuisance tripping caused by high ambient temperatures
• Can be reset immediately after tripping.
• The CBI SF range C/B terminals will house a cable diameter up to 50mm2 (European products up to 35 mm2)
The CBI SF Switchgear Range has been developed in Australia and South Africa specifically for Industrial,
Mining and Oil and Gas applications.
Safety is paramount
The four levels of protection provided by our RCBO’s are
• Sensitive earth leakage protection
• Overload protection
• Short circuit protection
• Safety isolation
CBI-electric: Australia
Free Call: 1800 770 870 | headoffice@cbi-electric.com.au | www.cbi-electric.com.au
CBI | technical news
04
Mining Circuit Protection
CBI-ELECTRIC LIGHT AND POWER DISTRIBUTION BOARDS
As a continued response to customer’s requirements, Heinelec Type HPR & HPS Heavy Duty Switchboards and HCF Heavy
Duty Load Centers were developed to meet the needs of Australia’s harsh mining requirements and increased safety
requirements demanded by our mining and other related customers.
The generous space within the HPR heavy duty switchboard, coupled with ergonomic design & removable sections allow
for easy access for equipment fitting & wiring.
CBI-electric: Australia
Free Call: 1800 770 870 | headoffice@cbi-electric.com.au | www.cbi-electric.com.au
05
CBI | technical news
Mining Circuit Protection
SHORT CIRCUIT PROTECTION
As discussed earlier it is a requirement that we provide protection against over-current and prospective short circuit at the
point of installation.
CBI provides miniature circuit breakers with an Interrupting Capacity of 6kA. Our Engineered solution using an upstream
MCCB (incomer on the DB) rated at 35kA changes the interrupting capacity to 30kA. That is the downstream breaker will
clear the prospective 30kA fault.
Ex: Isc=30kA rms & CABLE Z » 0
Cascaded systems will reduce initial cost and size, since downstream breakers are not fully rated for the prospective short
circuit fault current at their point of application. As we are using an engineered solution it is important to point out that all
replacement devices need to be identical or contact the manufacturer if unsure.
This method of protection is cited in AS 3007.2 – 2004 clause 4.5.3 (a) (ii) – The protection requirements for Electrical
Installations – Surface mines and associated plant.
REFERENCED DOCUMENTS
ASNZS: 3000:2007
AS/NZS 3001:200
AS 3007.2:2004
AS/NZS 3190:2011
AS/NZS 61008.1:2011
AS/NZS 61009.1:2011
CBI-electric: Australia
Free Call: 1800 770 870 | headoffice@cbi-electric.com.au | www.cbi-electric.com.au
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