Fluke 381 Application Note What’s Shakin’ With Your HVAC System?

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Application Note

From the Fluke Digital Library @ www.fluke.com/library

Troubleshooting

photovoltaic systems:

three typical problems

With the energy situa-

tion and problems in the

last few years has come

a major effort to increase

the amount of energy from

renewable resources. State

and federal government

policies in many areas

mandate increased use

of solar power. An HVAC

technician who is servic-

ing other equipment in the

building might encoun-

ter solar power systems.

Because the concepts and

arrangements of these

systems are new to HVAC

technicians, a short over-

view of the systems and

components is in order.

Photovoltaic systems convert

sunlight (photo) into electrical

power (voltaic). The sunlight that

strikes the semiconductor mate-

rial in the individual cells causes

electrons to move through a

wire. The electricity gener-

ated by photovoltaic systems

can be used to run a range of

equipment, from domestic appli-

ances to commercial production

equipment.

There are a number of vari-

ables in a PV system, but

ordinarily the PV array is

mounted on a roof that faces

the south as much as possible.

Obstructions are avoided. Note

that less power will be gener-

ated in the winter than the

summer due to the shorter days.

Also, maximum power will be

generated at midday rather than

in the morning or evening.

As part of the PV installa-

tion, some facilities provide a

real-time computer display that

shows the amount of energy

produced by the PV display, the

dollars saved, and the amount

of fossil fuel usage avoided. It is

great to know that facilities are

increasingly leading the way to

energy independence and low-

ering the amount of pollutants

released into the atmosphere!

The electricity generated by a

PV system may be used imme-

diately by that facility, stored, or

By Ron Auvil

in some cases sold back to the

local electric utility.

It is only natural for facilities

that have PV systems installed

to expect HVAC technicians to at

least know the basics. As these

systems become more com-

monplace we may be expected

to perform some basic trouble-

shooting of them.

Components of a PV

system

PV systems consist of the follow-

ing general components:

Individual cells. An indi-

vidual cell is a small part of a

PV system. A cell consists of

the semiconductor material, a

support structure, and a trans-

parent material that allows the

With the push to energy independence and renewable

energy sources, HVAC technicians need to know how

to troubleshoot photovoltaic systems

This electrical conduit connects a series of solar cell arrays.

2 Fluke Corporation Troubleshooting photovoltaic systems: three typical problems

sunlight to strike the semicon-

ductor material. The cell must be

physically tough as it is exposed

to the weather. The transparent

material that covers the cell also

must be stain and dirt resistant.

Each individual cell produces

only a few watts of electricity.

Modules and arrays. A

module consists of a number

of cells connected together

side by side. Modules may be

in either series or parallel, as

needed to obtain the desired

voltage and current. Since each

individual cell only produces

a small amount of electricity

large numbers of them must be

joined together to get significant

amounts of electricity. As may

be imagined, these modules can

become quite large and limited

by the size of the roof dedicated

to their use. Modules joined

together are then called arrays.

Wiring connects the individual

cells together to form these

arrays. The arrays are then

wired together to a central point.

Concentrators and combin-

ers. A concentrator or combiner

is a central wiring point for the

cells and modules. It represents

the aggregate power output

of the entire solar array. Even

though the output of each solar

cell is small, at the point where

multiple modules are connected

many amps of current are pres-

ent. Metering and conditioning

of the power may also take

place at the concentrator. The

concentrator is then connected

to either electrical storage or an

inverter. Storage may consist of

a large number of batteries.

Inverters. The power pro-

duced by a PV system is dc. The

vast majority of loads in a build-

ing are ac. An inverter is used

to convert the dc power created

by the modules into usable ac

power. The output of the inverter

may also be connected to the

local utility so that any excess

unused power is put back into

the grid and purchased by the

local utility to be used by other

customers. Metering and power

monitoring equipment are

installed here as well.

Since there are really few

components in a PV system

there are not many things to go

wrong. As mentioned previously

the major components are the

cells, modules, arrays, concen-

trator/combiner and inverter.

The PV system in the build-

ing may be providing power to

HVAC equipment or affecting the

power quality of the building.

This means that HVAC techni-

cians may need some basic

troubleshooting skills. (After all,

we are expected to know how to

work on everything on the roof

anyway, right?)

Three typical PV

troubleshooting

situations

In the examples below, the

person doing the troubleshoot-

ing is taking advantage of the

features of the new Fluke 381

Remote Display True-rms Clamp

Meter with iFlex™. While you

can use a true-rms ac/dc clamp

meter with voltage capabili-

ties for most of the work, we

used the Fluke 381 because

of its wireless feature (remote

readout and display), and the

iFlex™ flexible current probe.

The iFlex™ probe is absolutely

vital for troubleshooting these

photovoltaic problems. Since

large numbers of wires connect

each module and array to the

concentrator box, the junction

boxes are stuffed with individual

wires. The iFlex™ probe makes

the measurement of the individ-

ual module wires MUCH easier,

thus saving time and increased

accuracy.

Troubleshooting Problem #1:

Cell/Module/Array Problem

As with any troubleshooting

call, try to get as much infor-

mation from the customer as

possible. Try to find out when

the problem occurred and when

the last time the PV system

operated normally. Get as much

information, such as prints,

outputs, and wiring diagrams, as

possible.

A good place to start is to

check the output of the entire

system at the metering system

or at the inverter. Prior to getting

on the roof, check and record

the inverter’s input voltage and

current level from the array. If

the entire PV system is down

and not producing power it may

be an inverter problem. If the PV

system is operating at a reduced

power output the problem may

be one of the arrays or mod-

ules. You will have to trace out

the individual branch wiring

backward from the concentra-

tor. Again, the iFlex™ makes this

an easier job than it would be

otherwise.

A technician

attaches the iFlex™

flexible current

probe of a 381

Clamp Meter as he

prepares to trouble-

shoot a photovoltaic

system.

3 Fluke Corporation Troubleshooting photovoltaic systems: three typical problems

When you get up on the roof,

visually check the entire system

for any obvious damage. Also,

keep in mind that someone may

have disconnected the wiring

accidentally while servicing

another device on the roof. Once

the module or array that is not

producing power is found, check

all wiring, switches, fuses, and

circuit breakers. Replace blown

fuses and reset the breakers

and switches. Keep in mind

that since the PV system is on

the roof that a lighting strike or

power surge may have affected

it. With the large amount of

wiring present, check for broken

wires and loose or dirty con-

nections. Replace and clean as

needed. Especially be on the

lookout for wire nuts that are

connecting modules together.

They may have worked loose

and caused lack of contact.

The concentrators can be a

great place to troubleshoot the

system because the individual

wires from the modules are

brought back there. Each module

may have a fuse which should

be checked with the 381 meter.

Wiring problems and loose

connections may also cause a

particular module to produce too

low a voltage. Again, all wiring

connections should be checked.

If a particular module output

is low, it may mean that an

individual section of cells is bad.

These may be traced out using

the 381 meter at the junction

boxes until the culprit is found.

Any dirt on the modules, or

modules in the shade, can cause

a reduced output. Although the

modules are usually designed to

be maintenance free for years,

they may need to be cleaned.

Pollen can be a problem in some

areas of the country. Check the

system with the 381 meter after

any corrections are made.

Troubleshooting Problem #2:

Load Problem

Remember that the PV system is

used to operate building electri-

cal loads. Any problems with the

loads will affect the system as

well. The first step is to check

the load switches, fuses, and

breakers. With the 381’s voltme-

ter, check to see that the proper

voltage is present at the load’s

connection. Next use the 381

to check the fuses and circuit

breakers. If there are blown

fuses or tripped breakers, locate

the cause and fix or replace the

faulty component. If the load

is a motor, an internal thermal

breaker might be tripped or

there might be an open winding

in the motor. For testing pur-

poses plug in another load and

see if it operates properly.

As with any electrical system,

check for broken wires and any

loose connections. Clean all

dirty connections and replace all

bad wiring. With the power off,

check for and repair any ground

faults. If any fuses and break-

ers blow or trip again, there is

a problem short that must be

located and repaired.

If the load still does not oper-

ate properly, use the 381 meter

to check the system’s voltage at

the load’s connection. The wire

size may be too small and need

to be increased. It may also be

possible that that the wire runs

to the load are too long. This

will show up as a low voltage

at the load. In this case you can

reduce the load on the circuit or

run a larger wire.

Troubleshooting Problem #3:

Inverter Problem

Many HVAC technicians work

with variable speed drives every

day, so we are used to checking

ac and dc power. The inverter

in a PV system can also fail and

cause problems. The inverter

converts dc from the PV system

into ac power for building use. If

the inverter is not producing the

correct output first use the 381’s

voltmeter and dc ammeter to

check and record the inverter’s

operating dc input voltage and

current level. On the ac side, use

the 381 clamp meter to check

the inverter’s output voltage

and current levels. As men-

tioned previously, many of these

systems have a display that

To measure the current output of this photovoltaic cell, a technician wraps the 381iFlex™

flexible current probe around the conductor.

4 Fluke Corporation Troubleshooting photovoltaic systems: three typical problems

Fluke Corporation

PO Box 9090, Everett, WA 98206 U.S.A.

Fluke Europe B.V.

PO Box 1186, 5602 BD

Eindhoven, The Netherlands

For more information call:

In the U.S.A. (800) 443-5853 or

Fax (425) 446-5116

In Europe/M-East/Africa +31 (0) 40 2675 200 or

Fax +31 (0) 40 2675 222

In Canada (800)-36-FLUKE or

Fax (905) 890-6866

From other countries +1 (425) 446-5500 or

Fax +1 (425) 446-5116

Web access: http://www.fluke.com

©2011 Fluke Corporation.

Specifications subject to change without notice.

Printed in U.S.A. 3/2011 4014760A A-EN-N

Modification of this document is not permitted

without written permission from Fluke Corporation.

Fluke. Keeping your world

up and running.®

indicates current inverter and

system performance. Remem-

ber that the 381 clamp meter

produces a true-rms reading;

you can use the voltage and cur-

rent to measure and record the

kilowatt (kW) output. If possible

use the inverter display to show

the current total kilowatt hours

(kWh). You can then write down

this value and compare it to the

one recorded during the last

inspection.

If the inverter is not producing

the right amount of power there

may be a number of problems,

all of which can be easily

checked with the 381 meter:

• blown fuse

• tripped breaker

• broken wires

Also, use the 381 clamp meter

to measure the output ac side of

the inverter, because the load

on the inverter might have a

current demand that’s too high.

Your choice then is to reduce

the loads or install a larger

converter.

With the power off, check for

and repair any ground faults

before starting the inverter

again.

Remember that the inverter

may be tied into the local utility.

The ac current output from the

inverter fluctuates with the level

of solar input on the array. The

inverter maintains the correct

output voltage and phase to the

utility. Any voltage problems

from the utility may cause the

inverter to shut down. In this

event contact the utility for

repairs.