Short-Circuit Current Ratings and AC Drives

Short Circuit Current Ratings and AC Drives

Ivan Spronk, Product Marketing AC DrivesSchneider ElectricIndustry NOW Express

2Schneider Electric - Industry Business – Short Circuit Current Ratings and AC Drives – 2012

Goal of this session ●

Understand

●

Importance of proper SCCRs

●

Hot button points and confusion about SCCRs

●

Be able to articulate the various aspects of SCCRs

●

Understand

●

The information Schneider Electric provides

●

The information most competitors provide

●

Be able to position yourself to help your customers

●

Know what documents to use to find SCCR for the Altivar

product line


Why are these ratings important?


Why are these ratings important to you?

● Applying SCCRs

properly can:

● Enhance personnel safety

●

Limit equipment damage

●

Reduce lost production time

●

Provide the most cost effective solution


Hot Buttons & Points of Confusion

●

Recent changes to NEC and UL508●

Control panels are now required to have a SCCR●

Increased industry attention to SCCRs

●

UL 508C: test standard for AC Drives●

Lacks specific test method for short circuit testing●

Leads to different interpretations by manufacturers●

Not all manufacturers publish the same info●

Allows for a “higher must be better”

mentality

●

Who is impacted the most?●

Those not performing tests on each design:●System integrators●Panel builders●

OEMs


Aspects of SCCRs●

Circuit breakers and fuses●

Designed to operate at some level of short circuit current●

Designed to interrupt current● Common values: 1k, 5k, 10k, 22k, 42k, 65k 100k

●

These are overcurrent

protective devices (OCPD)●

Has an AIR

rating: ampere interrupting rating

●

Other electric equipment panels and products●

UL requirement: ● Have a maximum short circuit current rating

●

Designed to operate at some level of short circuit current● Common values: 1k, 5k, 10k, 22k, 42k, 65k 100k

●

Rating can be no higher than lowest rated product●

Equipment and panel need to safely withstand the level


Aspects of SCCRs and AC Drives

●

Input section●

Available short circuit current has a thermal impact ●

True for any device converting AC power to DC power

●

Internal section●

Internal of an AC Drive has many current paths●

AC Drives should not be tested like starters

●

Output section ●

Have IGBTs

that turn off at high current level●

Many suppliers provide SCCRs

based on testing the output


Aspects of SCCRs and AC Drives: Schneider

Electric Position

●

Input section ●

Customers need to know the level of available short circuit current the drive was designed to handle

●

Internal section ●

Short circuit testing should test the most vulnerable part

●

Output section ●

A SCCR should not be based on the output


Information provided by Schneider Electric: Input Section●

Input Section: ●

The input current

increases as AFC

increases● AFC = amount of available fault or short circuit current●

True for any devise converting power

●

The input AFC rating reflects:●

Available short-circuit current at input terminals that the drive was designed to operate both thermally

and electrically

●

How much effect do various levels have?●

See Data Bulletin 8800DB0801 for more info

●

Schneider Electric designs to UL recommended levels

●

Schneider Electric provides this input AFC rating●

If the available prospective short circuit current exceeds the level the drive was designed for, use externally mounted impedance to reduce level

–

Line reactors are commonly used –

DC chokes


Information provided by Schneider Electric: Internal Section

● Internal Section: ●

AC Drives contain many power components● Diodes● Capacitors●

IGBTs

● There are multiple paths for a short circuit

●

Internal components may short across the power circuit.

● To obtain a SCCR, Schneider Electric performs ● A breakdown of components test● Testing the most vulnerable parts ● At the marked SCCR value

Why do other manufacturers only test and provide a SCCR based on shorting the out put of the drive?


Information provided by Schneider Electric: Internal Section

●

Why do other manufacturers only test and provide a SCCR based on shorting the output of the drive?

●

Left over from the legacy test method for a motor starter

●

For a starter or contactor●

Shorting the output tests this entire device

●

Many drive manufactures are currently providing a SCCR based on only testing by shorting the output ●

Schneider Electric has taken an industry leadership position●

Providing SCCR ratings based on internal breakdown tests●

Leading UL 508C to mandate an internal breakdown tests

Electric Company / Distribution Panel

Load


Information provided by Schneider Electric● Internal Section:

●

Schneider Electric SCCR parameters validated during Breakdown of Components testing

●

Contain a breakdown within its enclosure based on the Available Fault Current (AFC) and its listed Overcurrent Protective Device

(OCPD)●

Should not create shock, flame, fire or expulsion hazard outside

the enclosure

●

Schneider Electric provides a rating for a wall mounted AC Drive● AC drive with optional conduit entrance● Housing of the unit must contain the hazard

●

Schneider Electric provides a rating for an AC drive mounted in an enclosure

●

Enclosure around the drive must contain the hazard

●

See ANNEX document


Information provided by Schneider Electric: Output Section

●

Output Section:●

Today’s IGBT technology used by most manufactures● Will turn off well before fault current builds to dangerous levels

–

Interrupting 100kA on the output is no issue●

Drive input does not see fault current

●

Available input short-circuit current and output interruption rating are unrelated

●

Schneider Electric provides this information only to show our product can obtain the same rating on the output

●

Testing the output does not help construct a robust solution


Aspects of SCCRs and AC Drives: our position

●

Input section ●

Customers need to know the level of available short circuit current the drive was designed to handle

●

Internal section ●

Short circuit testing should test the most vulnerable part

●

Output section ●

A SCCR should not be based on the output


What information do competitors provide?●

ABB provides:●

Input currents with and without line reactors with no explanation

●

Specifying expensive Class T fuses only

●

No circuit breaker ratings

●

Schneider Electric provides:●

Multiple ratings with circuit breakers and GV2

●

Ratings with Class J fuses

● 25-50% less expensive than Class T fuses


What information do competitors provide?

●

ABB●

Claiming maximum 200k SCCR rating●

Clearing relying on testing only the output of the drive

●

Claiming actual rating is based on OCPD

●

Providing no information about thermal impact of various levels of available fault current

●

Schneider Electric provides information about:●

Thermal impact of various levels of available fault current●

Multiple ratings with circuit breakers and GV2●

Ratings with Class J fuses


What can you do with this information?●

Assist customers to build equipment that can●

Enhance personnel safety with ratings on product match installation

●

Limit equipment damage●

Properly rated to contain a short circuit

●

Reduce lost production time ●

Properly rated to contain a short circuit

●

Provide the most cost effective solution● Install just what is needed●

Control panel cost is proportional to specified SCCR

●

Schneider Electric is leading the industry in this effort by challenging the information being supplied by others


Resources Know which Codes & Standards apply to your customer’s equipment

●

NEC2011 Article 409.110 and 430.8●

Requires that industrial control panels be marked with (SCCR)●

Requires AC Drives be rated with a SCCR

●

UL508A points to UL508C for power conversion controllers●

i.e. AC & DC power converters or drive controllers

●

UL 1995●

Standard for Air Conditioning and Refrigeration Equipment

●

UL508C ●

Provides a method of establishing SCCR for Drives ●

Provides a SCC rating that satisfies NEC

requirements.

●

Issues being worked with UL508C ●

The standard lags technology changes.●

As such the test methods have room for interpretation.●

Most are publishing only an output short circuit rating


Resources ●

SCCR ratings for each Altivar

product line●

Each product line has a document listing SCCRs

●

The Effects of Available Short Circuit Current on AC Drives●

Data Bulletin 8800DB0801

●

Variable Frequency Drives and Short Circuit Current Ratings●

Data Bulletin 8800DB1203 coming soon

●

Control Panel Technical Guide●

How to ensure trouble free approval of your UL complaint control panels

●

CPTG005_EN


Summary●

Short-circuit ratings allow to:

●

Have safer installations

● Minimize equipment damage

● Improve up-time in the most cost effective way


A 5HP AC drive…. 5 kA Isc, without Line Reactor, Ipeak=27.2

Time

500ms 510ms 520ms 530ms 540ms 550ms 560ms 570ms 580ms 590ms 600msI(L1) RMS(I(R8)) RMS(I(L1))

-40A

-20A

0A

20A

40A


Time


-60A

-40A

-20A

-0A

20A

40A

60A




Time


-80A

-40A

0A

40A

80A


Altivar 61 Annex


ABB ACS355 ●

specifying expensive Class T fuses


ABB ACH550 UH

●


ABB ACH850●

now providing Input current with and without line choke

●

Class T fuses


AB PowerFlex 40P

●

“actual SCCR = AIC of installed fuse / circuit breaker

●

claiming 100k SCCR


AB PowerFlex 700 ●

“actual SCCR = AIC of installed fuse / circuit breaker

●

claiming 200k SCCR


Internal Break Down of Components Tests


Typical available fault current at various points and appropriate SCCR rating


Codes and Standards: UL508C says:47 Short Circuit Test – High Fault Currents

47.1 When any models within a drive series are intended to be rated with high fault current values in excess of the standard current values required by Table 45.1, then one representative model from those intended to be rated with high fault current values shall be used for testing. This representative model shall be subjected to only one high fault current short circuit test.

Exception: A drive series complies with the High Fault Current Short Circuit Test in this section without additional testing when:

a) The drive series uses solid state short circuit protection circuitry for compliance with the Short Circuit Test, Section 45; and

b) The solid state short circuit protection circuitry is used in accordance with 45.1.3.

●

Most Drives Manufactures take this exception!●

Schneider Electric does NOT●

Schneider Electric conducts short circuit testing at the marked short circuit current rating


UL 508 C: Minimum Short Circuit Test Values


Thank You!

Technology

Short-Circuit Current Ratings and AC Drives