PLS - Loose Connections

7/30/2019 PLS - Loose Connections

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SolutionsowerLogicSolut ions

The Problem

Last June, an office building in a large industrial complex beganexperiencing unexpected rebootings of personal computers. Also, someof the fluorescent lighting in the building was flickering. The problemhad been occurring for an hour before a frustrated employee reported

it to the facility engineer. Suspecting

utility power quality disturbances, theengineer immediately returned to hisoffice to check the plants powermonitoring and control system.

The facility had recently installed aPOWERLOGIC system capable ofcapturing voltage and currentwaveforms. The system included circuitmonitors at key locations within thecomplex, including one CM-2350 at theservice entrance of the building that wassuffering the intermittent reboots.

Noting that his workstation software wasindicating an alarm on the officebuilding circuit monitor, the facilityengineer interrogated the CMs on-board memory. He found that it had

captured multiple voltage fluctuations on phase A-to-neutral. Voltageon this phase dropped below the 88% threshold intermittently over thepreceding hour (see figures 1 and 2).

The office building was served by an overhead 12 kV circuit owned andmaintained by the local utility. This feeder served the office buildingand other commercial andsmall industrial customerslocated beyond the plant.

Volume 1, Issue 2 Loose Connections Cause

Power Quality ProblemsIn This Issuewediscuss the needto eliminate looseconnections in acpower systems, inorder to reduce

the voltagefluctuations thatcause powerquality problems(and equipmentdamage).

Figure 1: Voltage fluctuations show the cycle-by-cyclevoltage drop on phase A-N, which caused equipmentmisoperation and lighting flicker.

Figure 2: Waveform capturetranslated into effective(rms) values shows thevoltage fluctuations onPhase A-N due to thefaulty utility switch.


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Power Management

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presents a common

power system

problem, and offers

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low as 0.5% can cause a perceptible flicker insome lighting sources. Though individualsvary widely in their susceptibility to lightflicker, it is extremely irritating to someworkers, resulting in decreased productivityand increased re-work. Studies show thatsensitivity depends on the amount ofillumination change (magnitude), how often itoccurs (frequency), and the type of activityundertaken. The problem is furthercomplicated by the fact that lighting systemshave different response characteristics to

voltage changes.

The Solution

For the industrial complex in this case history,the solution to a loose connection problemwas to call the local utility. The company senta line crew to the scene to investigate thereport. By the time the crew arrived, molten

o AMMETER (A)

o VOLTMETER,L-L(V)

o VOLTMETER,L-N (V)

o WATTMETER (W)

o VARMETER (VAr)

o VAMETER (VA)

o POWER FACTOR METER

oFREQUENCYMETER (Hz)

o DEMAND AMMETER (A)

o DEMAND POWER (W)

o DEMAND POWER (VA)

o WATTHOUR METER

o VARHOUR METER

o THD, CURRENT (%)

o THD, VOLTAGE (%)

o K-FACTOR

[CT:5]

[PT:120]

[Sys. Type]

[Dmd.Int.]

[WH/Pulse]

[Address]

[Baud Rate]

[Nom.Freq.]

[Reset]

[Reset]

[Reset]

[Reset]

[Reset]

[Rst.Min/Max]

[Set Password]

[Accept]

3-PHASE

A(A-B)

B(B-C)

C(C-A)

N

SELECTMETER[Value]

METERS

MIN

MAX

ALARM

[Setup]

Kilo

Mega

PHASE

MODE

Figure 3: The office building in this case history was served at 480 V from anoverhead 12 kV utility distribution system.

Circuit Monitor Inside

Switch Location

Utility Transformer

UndergroundFeeder toTransformer

Figure 4: A three-pole knife blade switch beganarcing due to improper seating.

Suspecting that thevoltage sags resultedfrom problems onthe utility system,

the facility engineercalled the local utility.Then an employeeat the office buildingreported seeing awelding light atthe top of the utilitypole just outside thebuilding. Figure 4shows that thewelding lightcame from onephase of a 3-pole

knife-blade switchmounted justupstream of the feeder serving the building.

By this time, the arcing problem had escalatedto the point that personal computers wererebooting, lights were flickering badly, and thelocal area network server was malfunctioning.The facility engineer placed another call tothe utility to report the arcing.

Key Concepts and Terms

Voltage FluctuationsVoltage fluctuations are defined as systematicor random variations of voltage. Fluctuationscause cycle-by-cycle changes in voltage whichcan come from a variety of sources. Arcfurnaces are one of the most common causesof voltage fluctuation. These furnaces canoften affect other customers served from thesame utility circuit. Loose connections,frequent motor starting or intermittentloading (as may occur with a chippermachine), and welding are common sourcesof voltage fluctuation inside commercial andindustrial facilities. Loose connections form

high impedance points in the electrical systemwhich cause intermittent voltage drops. Thefluctuations affect equipment on the load sideof the loose connection. Inside a facility, looseconnections can occur wherever conductorsterminate or transition.

Light FlickerSensitive equipment disruption and powersystem component failures are only part of theproblem. Voltage fluctuation magnitudes as


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1997 Square D All Rights ReservedBulletin No. 3000HO9502 10M DL 3/98

POWERLOGIC, SQUARE D, and areRegistered Trademarks of Square D Company.

Square DsPowerManagementOperationoffers completepower quality consulting services to

ensure that power problems do notimpact your operation. Contact ourpower management experts forinformation about the following:

Power Quality Consulting

Energy Management Consulting

Harmonic Filters

Power Factor Correction

Power Management Training andTechnical Support

Digital Simulation Studies

Remote Monitoring Services

Data Collection and Analysis

Our number is 1-888-PWR-MGMT.

Some devices indicate the actual temperatureof the metal components.

While periodic infrared scans are strongly

recommended, their benefit in preventingloose connections problems is limited. M anycompanies complete the surveys on an annualor biannual basis. The problem may continuefor months, intermittently disrupting sensitiveproduction equipment or reducing employeeeffectiveness, before the periodic scandiscovers it. The scan also relies on thesecondary effect of loose connections:excessive heating. The heat is caused byunusual voltage drops across circuitcomponents not intended to be highimpedance connections.

POWERLOGIC systems continuously monitorfor the voltage fluctuations that are the cause ofheating and equipment problems. The systemscapture a variety of other power-relatedproblems as well, but can easily pay for them-selves by preventing a single loose-connectionincident like those described earlier.

Conclusion

Some experts claim that most power qualityproblems can be solved with a screwdriver.What they mean is that wiring and grounding

problems like loose connections cause thegreat majority of operating problemsexperienced by sensitive equipment.

Ensuring that loose connections do notdisrupt your facility is more complicated

than just tightening lugs with a screwdriver(and needs to be safer!). One importantway to ensure that voltage fluctuations fromany source do not disrupt production, orcause catastrophic faults, is to monitor yourelectrical circuits.

POWERLOGIC Circuit M onitors can capturevoltage fluctuations, as well as other phen-omena that disrupt or damage equipment.The system provides the plant engineer with

the information needed to reduce downtime,ensure employee productivity, and reducemanufacturing costs.

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PLS - Loose Connections