a review on faults and detection techniques in photovoltaic … · 2019. 5. 3. · a review on...

A Review on Faults and Detection Techniques

in Photovoltaic System Supriya S.Kharage,1Pragati N korde2

ElectricalDepartment12

G H Raisoni Institute of Engineering and Technology,

WagholiPune,India12

[email protected] [email protected]

Abstract—

PV system are associated with different types of faults. They directly affect the output of the PV system. Hence PV array protection is one of the main aspect to enhance the efficiency and reliability of the system. Despite the fact that

PV systems have no moving parts and usually require low maintenance, they are still subject to various fault conditions. Especially for PV arrays (dc side), it is difficult to shut down PV modules completely during faults, since

they are always energized by sunlight in daytime. Furthermore, conventional series-parallel PV configurations increase voltage and current ratings, leading to higher risk of large fault currents or dc arcs. This paper focuses on Different types of faults in PV system, there causes and Faults detection techniques.

Keywords— PV Faults, Fault detection, Ground fault, Line to line fault, GFDI, OCPD

I.INTRODUCTION

Electricity demand is increasing day by day. Demand fulfilment is one of the major task in Power

system. Solar system plays vital role to fulfil the demand. Also solar system has advantages that renewable

energy source, clean energy, ad abundant availability, due to electricity generation by using PV Plant is more

popular in now days. The rapid development reveals some technical issues, PV system associated with different

types of fault, among the numerous possible faults such as ground fault, line-to-line fault, hot spot formation,

polarity mismatch, arc fault, open fault, bypass diode failure, and dust/soil formation in a PV array, ground fault,

line-to-line fault, and arc fault are reported to be the major reasons behind catastrophic failures resulting in

electrical fires.[1] These fire hazards not only show the weakness in conventional fault detection and protection schemes in PV arrays, but also reveal the urgent need of a better way to prevent such issues. In this paper

discussed about different types of faults, in PV array, causes of faults, conventional and existing detection

technique for fault in PV array.

II.FAULTS IN PV ARRAY

As shown in Fig.1, a typical grid-connected PV system consists of several major components, including

the PV modules as power sources, power conditioning unit (i.e., PV inverter) integrated with MPPT algorithm,

electrical connection wirings, and protection devices, such as OCPDs and ground-fault protection devices

(GFPDs).

Several types of fault could happen inside PV arrays, such as line-line faults, ground faults, open-

circuit faults, and mismatch faults. Among these faults, line-line faults and ground faults are the most

common faults in solar PV arrays, which potentially involve large fault current or dc arcs. [2].

III. CAUSES OF FAULTS

A ) Line-to-Line Fault:

A line-to-line fault involves high fault current or DC arcs between two different potential points in the PV

array . Such fault is defined as accidental short-circuit between two different potential points in an array. It

can occur among modules that belong to the same string or between two adjacent strings. A line-to-line fault

in addition can occur between array cables of different potential, but it doesn’t not involve any grounded

points. In some situations, the line-to-line fault is called a bridging fault when it occurs between two

modules of same order from two different strings. The fault causes a reduction in open-circuit voltage, but

JASC: Journal of Applied Science and Computations

Volume VI, Issue V, May/2019

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mailto:[email protected]

short-circuit current may stay the same. The voltage reduction will result in changing the V-I characteristics

of the PV array.[4]

Fig. 1Schematic diagram of a grid-connected PV system, including various types of faults in the PV array[3]

B) Earth or Grounding Faults:

A ground fault happens due to unexpected short-circuited path involving one or more currying current

conductors and the ground, which would cause a huge increase in the current passing through the affected

conductors causing mismatched currents and changes of the PV array configuration. The consequences of

ground fault are subsequent fault currents, disturb or drop output voltage, and suddenly changes in the V-I

characteristics of the PV array. Ground faults are considered the most common faults in the PV system. A

breakdown or failure of cable insulation due to manufacturing defects or overheating and aged cables may cause

such faults. Ground fault may result in a number of hazards such as electric shocks and fire hazards. [4]

C) Open-Circuit Fault:

This type of fault occurs when a disconnection problems appear in a PV string or more. Most of the

disconnection problems are due to poor soldering in strings interconnections. Short circuit current and

maximum power are decreased due to the open-circuit fault, while open voltage stays close to its normal value

[4]



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D) Mismatch Fault:

Mismatches in PV modules occur when the electrical parameters of one or group of cell are significantly

changed from other. In addition, mismatch faults are caused by interconnection of solar cells or modules, which

experience different environmental conditions (i.e. irradiance or temperature) from one another. Mismatch faults

are the most common type of fault compared with Earth fault and bridging faults, among PV arrays. Mismatch

faults may lead to irreversible damage on PV modules and large power loss. However, they are difficult to detect

using conventional protection devices, since they generally do not lead to large fault currents. These faults can be

categorized into two groups, permanent and temporary. Their causes are listed below:

a) Temporary Mismatches: are divided in two groups:

• Partial shading: Shading effect occurs when a part of the panels array are shaded which can be caused by a number of different reasons, like shade from the building itself, light posts, chimneys, trees, clouds, dirt, snow and

other light blocking obstacles. Non- uniform temperature: Snow covering,

b) Permanent Mismatches: • Hotspot: Hot spot heating occurs when a module’s operating current exceeds the

reduced short circuit current of a shadowed or faulty cell or group of cells within the module . To create a Hot spot

fault, a variable resistor in series with the Rsn of each defective cell could be added in Simulink. Value of this

resistor is considered approximately one until five ohm.

• Soldering: this defective appears in resistive solder bond between cell and contacted ribbons.

• between cells and contact ribbons, Degradation: • Discoloration;

• Delamination;

• Transparent layer crack [5]

IV. FAULT DETECTION TECHNIQUES.

A) Conventional Fault Detection Technique

Conventional fault detection and protection uses ground-fault detection interrupters (GFDI) and

overcurrent protection devices (OCPD), A PV array ground fault is an electrical pathway between one or

more array conductors and earth ground. Such faults are usually the result of mechanical electrical, or

chemical degradation of photovoltaic (PV) components, or mistakes made during installation. Fault

types are defined by the location in the array and the impedance of the fault and can vary widely in

the severity of their impact on array operations depending on these two factors. In order to protect the array

during a ground fault event, a ground fault protection device (GFPD) is used to detect ground fault

currents. If the GFPD or another device also interrupts the fault current, the protection system is called

a Ground Fault Detector/Interrupter (GFDI). The 2014 National Electrical Code (NEC) 690.5 specifies

ground-fault protection requirements for grounded direct current (DC) photovoltaic arrays while NEC

690.35 defines the requirements for ungrounded systems. Both of these sections require ground faults are

detected and their presence is indicated.[6]

For protection against over current Over current protection device (OCPD)is used. fuse requires 2.1Isc

of a PV module. However, due to current limiting nature of PV arrays, nonlinear I-V characteristics, high

fault impedances, MPPT action of inverters or PV grounding arrangements faults in PV array may not be

cleared. In addition, some factors such as environmental conditions (varying irradiance level and

temperature), winter season, PV array configuration and fault location, degradation, shading, hot-spot and

MPPT effect makes fault analysis complicated and hence conventional string protection devices may not be

able to clear fault correctly. [7]

B) Existing Fault Detection Technique

This study focused on solar photovoltaic fault diagnosis. Chaotic synchronization system was

combined with extenics for fault diagnosis. However, the classical domain cannot identify the fault state

accurately as long as the irradiance and temperature have changed. This study uses BP neural network, so as

to remedy the defect of unavailable diagnosis when the irradiance and temperature change, and uses the center

of error dynamic trajectories of two chaotic subsystems as eigenvalue, to overcome the decrease in diagnostic

rate that resulted from under voltage at low light level.[8]This approach was developed and validated using

historical measurements from a 120-kW PVplant located in Toronto, Canada. The fault detection algorithm



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was validated with data that include measurements taken during an actual faulty operation of the PV system-a

period of time when the inverter was malfunctioning. The model consists of one equation that uses solar

irradiance and PV panel temperature measurements to predict the ac power production. In order to determine

if this simple model is sufficiently accurate, its predictive performance was compared to that of a neural

network model. Two approaches were tested for developing the models: an approach involving separate

models for different irradiance ranges, in order to better represent the PV system performance at different

sunlight levels, and a global approach over all irradiance values.The measurement

samplingratewas10min;thesemeasurements were also averaged over 1 h, to determine if this will lead to an

improved model accuracy and fault detection rate. The performance ratio (PR) was used to complement the

model-based fault detection approach, by keeping track of the long-term performance of the PV system.

Based on the results, recommendations for online implementation were formulated.[9]By analyzing the

details and features of power losses between the expected and actual values, reference [20] is able to detect

broken cells in a PV module. [10]

In this paper, we propose a photovoltaic (PV) energy conversion system (PVECS) fault detection scheme

using a fractional-order color relation classifier in microdistribution systems. Based on electrical examination method, output power degradation is used to monitor physical conditions with changes in a PV array’s circuitry, including grounded faults, mismatch faults, bridged faults between two PV panels, and open-circuit

faults.[11]This paper deals with the problem of supervising and monitoring a photovoltaic (PV) plant. First,

an offline descriptive and inferential statistical procedure for evaluating the goodness of system performance is presented. Then, an online inferential algorithm for real-time monitoring and fault detection is

introduced.[12]The monitoring and diagnostic methodology discussed in this paper is mainly focused on the

development of paradigms for the assessment of accidental causes leading to efficiency losses, such as shadows, and PV panel dirtying and aging phenomena, which can seriously compromise the PV panel

behavior.[13]—In this paper, an innovative sensor suited to perform real-time measurements of operating

voltage and current, open-circuit voltage, and short-circuit current of string-connected photovoltaic (PV)

panels is presented [14].Different estimation method based on the iMPPT method [15].Reference [16]

presents a scheme for islanding detection of grid-connected PV systems, which is based on negative sequence

active and reactive power variations at the coupling bus. A hot spot detection method based on AC parameter

characterization is proposed in [17] for detecting hot-spot heating within cells of a PV panel. Reference [18]

diagnoses arc faults by calculating the modified Tsallisentropy of the PV panel current. These methods mainly focus on detecting PV faults other than LL and LG faults. A cost-effective scheme to detect the internal

resistance change of a PV array is introduced in [19], which uses the signals available in the extremum-

seeking control (ESC)-based MPPT method. Internal resistance changemight be useful for identifying

abnormaloperations of PV systems. However, the scheme needs future development to detect faults. The time

domain reflectometry (TDR) approach to detect faults, which injects a signal into the circuit and observes the response of this signal to detect impedance changes, is introduced in [20] and [21]. The accuracy of this

method may be significantly influenced by the set of selected signals, and the response of an incident signal might vary in PV systems with different materials, configurations and operating environments. A PV health monitoring system based on probabilistic neural network (PNN) is proposed in [22],

A fault detection algorithm for PV systems based on pattern recognition and machine learning

techniques is proposed to improve the detection accuracy for challenging L-L fault scenarios that occur under

low irradiance, through a high impedance, or in inter action with the MPPT scheme. The method takes

advantage of the MSD technique to extract the feature space of L-L faults. A two-stage SVM classifier is proposed for decision making. Both simulations and experiments are carried out in [23]. The proposed fault

detection scheme is based on a pattern recognition approach that employs a multiresolution signal

decomposition technique to extract the necessary features, based on which a fuzzy inference system

determines if a fault has occurred. The presented case studies (both simulation and experimental) demonstrate

in [24]



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V.CONCLUSION

This paper discussed about the different faults in PV system, there causes and detection technique. GFDI and

OCPD are the conventional fault detection technique have some draw back with system changes. Existing

fault detection technique overcome these draw back with little extend. But also there is some protection gap. It

reveals that need of better technique to overcome this protection gap.This paper will help the researchers and

practicing engineering to understand the faults occurring in PV arrays and the use effective fault detection

techniques to deal with them.

VI.REFERENCES

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