Scope
Once the inspections and tests specified for the given PV plant are successfully completed with satisfactory results, DEWA issues the Connection Agreement, which certifies that the installation complies with DeWa's rules and regulations and that electricity production can begin. Particular attention will be paid, in this document, to the modalities for carrying out the tests, since Inspection is a task that is usually carried out by DEWA Engineers, or by those of the relevant Authority in terms of Mechanical Inspection.
Defnitions
In this latter situation, the Renewable Generating Unit referred to in the Standards is the part of the Plant that is able to produce energy without input from non-renewable sources. Verification – all measures by which the compliance of the electrical installation with the relevant standards is checked (NOTE: includes inspection, testing and reporting).
Acronyms and Terminology
According to the Standards [1], the following on-site tests (and inspections) must be carried out on RRGUs / RRGPs before and after connection to the distribution network. Test (and inspection) without interconnection with the network to check the consistency of the system.
General Requirements
Performance test and post-connection inspection are required only in case of RRGPs with maximum capacity PMC ≥ 100 kW.
Methodology of the Tests
Design Documents for the Inspection
Test Engineer
The test engineer, delegated by the applicant, must be certifed by DEWA Reporting
Safety Issues
Very low temperatures or strong winds due to the difficulty in gripping and holding tools. However, this is not valid for the installation of a solar system, because exposing a PV module to sunlight creates a voltage between the terminals of the module itself. To avoid this, one can short-circuit both connectors on a PV module or on a series of modules (the short-circuit current does not damage the PV modules because it is only slightly larger than the rated current).
Another possible remedy is shown in Figure 4 and consists of keeping the connectors of a module and the string protection switch open during installation. Alternatively, a person touching two poles on the same branch is not safe (cases B and C). In all cases, the work and interventions during the construction and during inspection and maintenance of a PV generator are considered as live work/interventions.
When the PV system is installed on a roof, operators must take the safety measures prescribed for the given conditions, for example a safety harness anchored with a carabiner to a stable element of the roof (hooks, safety ropes, pillars, etc.). Bees, hornets and other insects can nest behind a PV panel or in another sheltered place. More information on the potential hazards associated with working with solar PV equipment is available in the document “People Safety: Recommendations for DRRG solar PV systems” [4].
Information from Applicant about Specifc Risks on-site and Safety Measures
When modules are exposed to solar radiation, they can reach temperatures of almost 100 °C at the front and up to 80 °C at the back.
Methodology
Inspections
Tests
Check the average string voltage and current related to each string combiner box: in the case of strings with deviations greater than ± 5% from the average, the continuity of the connected circuits should be checked first, then the string voltage/current should be rechecked. Test strings belonging to the same combo box in quick succession to minimize the effects of solar radiation variations. Measure each individual wire with the (+) and (-) poles shorted and grounded (other sets are open).
The limit value of the insulation resistance for the acceptance of each string is ≥ 40 [MΩm2] / S (where S is the total surface of the PV modules of the string in m2) with a minimum of 5 MΩ in dry conditions and 2MΩ in wet conditions. It is worth noting that measuring the ISC string current (test no. 2b) and testing the insulation of the string to ground (test no. 3) can be dangerous if not performed properly and carefully; recommendations are highlighted in the following paragraphs. The Consultant/Contractor will need to check the quality of cabling and wiring and connections well before all installations are completed.
DEWA inspectors will have the opportunity to assess the quality of the installations and if necessary ask the Consultant/Contractor to improve the quality. DEWA and the Owner will have feedback on the performance level of the Consultant/Contractor. Details of each verification provided for in the Mechanical Finish Inspection as specified in Standards [1] are described in the following paragraphs.
Mechanical Tests (and Inspection)*
- General Assessment of RRGU/RRGP
- Civil Works
- Support Structures
- Photovoltaic Modules
The inspections listed below will involve the competent Authority/Entity (i.e. Dubai Municipality, Trakhees, Etihad Esco etc.). A preliminary description of the Inspection is given only to make the Applicant aware of the type of control that may be carried out.
Inspection without interconnection
- Electrical Equipment
- Protection of Assembled Components (e.g. IP degree)
- String Combiner Boxes (DC string connections and AC auxiliary services)
- Electrical Power Connections in Substations and Electrical Rooms
- Bonding and Earthing System
- Connections to Earthing System of Metal Structures/Equipment
Based on 100% of the installation, check the compliance of the labels (cables, clamps and connectors) with the drawings and project documentation. The earthing busbar is properly connected to the local earthing of the site f) Independent earthing connection of the main equipment to the earthing busbar .. g) Connection of earthing copper cables to aluminum structures through suitable connectors (copper-aluminium, galvanized copper, stainless steel, etc.) .) to prevent corrosion due to various metals.
Tests without interconnection
- Insulation of LV connections DC and AC
- Measurements on PV strings
- String Insulation to Earth
- Calibration of Protections (Interface Protection)
The test to be performed on each string with the (+) and (-) poles short-circuited and connected to ground (the other strings are open) by applying a test voltage of 1000 VDC maximum for 1 minute. Note: Protective devices and electronic equipment that may be affected by the test voltage must be disconnected when making measurements. Earth cord insulation testing can be dangerous if not done properly and carefully.
In particular, the connection and disconnection of the (+) and (-) poles must be carried out using a suitable one-way disconnect switch. Alternatively, the test can be performed in the dark or by covering the front of the PV modules. Measure each individual string for short and ground (other sets of the same combo box must be open).
Insulation resistance limit value for acceptance of each string: 5 MΩ in dry conditions (2MΩ in wet conditions). However, it is required that the settings be checked locally and if necessary, the said settings should be adjusted. Check the correct settings and interference of the Interface Protection(s) through simulated tests using the methods and equipment described in Appendix D.1.4 and D.2.5 of the Standards [1].
Methodology
Verification of the connection of energy meters. a) Find out the nameplate data of all voltage and current transducers. Check the correct operation of alarms and messages through simulated intrusion tests (blank tests). Check system operation, measurement reliability and compliance with requirements. a) Check calibration and certification of meteorological sensors.
The test is performed for each inverter and associated series of PV modules. a) Measurement of the power consumption to the inverter with a DC wattmeter (including voltage and current). Measurements should be performed simultaneously or in rapid sequence for each subsection (inverter) of RRGU.
Functionalities of RRGU / RRGP
- Connection to Grid and Start-up of RRGU /RRGP
- Parallel with the grid
- Start-up Tests on Inverters
- Verifcation of Connection of Energy Meters
- Alarms and Messages
- Measurements
- RRGU /RRGP Monitoring System
- Operation of Electrical Systems in each cabin
This part of the tests is devoted to verifying the degree of accuracy of the measurements carried out by the instruments on board any equipment. Referring to the size of the DRRG, a monitoring system can be installed to facilitate the management of the PV plant. According to the plant size, such a monitoring system will be managed by the Consultant/contractor, the Owner or by the entity appointed for the "Operation and Maintenance" service.
The test allows verification that the monitoring system is in accordance with the design, the operation of such a system and the reliability of the measurements. The verification of solar sensors should ensure that the sensors and instruments of the PV plants are reliable and ensure that the performance of the PV plant can be evaluated at any time within the operation of the PV plant. The appropriate behavior of the electrical systems in each cabin, both for power and auxiliary systems, should be verified.
The checks are carried out by verifying the correct functioning of such systems through their instruments, in particular to assess the absence of warning or error messages.
Verifcation of the Technical Dossier
Performance Tests and Post Connection Inspection
Performance Tests
- Harmonic Emissions
Measurements of the temperature of the PV module using the temperature sensor located on the rear side. Pnom = PV generator rated power [kW] (Total rated power of installed modules) @ STC. 2 ) the sensor is flush with the surface of the modules (accuracy equal to or better than ±5%). The performance test results will be described in a separate document and a copy of this test will be made available to DEWA before a post-connection inspection can be carried out.
State affiliation and signature of the person(s) undertaking the measurements, and those participating in the test (if any). Description of the tests, the parts of the PV plant tested, and the results of the related performance tests. N2 = number of 10-minute intervals in which the THD value for one or more of the phase voltages exceeds the voltage limit defined in [1] and the supply voltage is within normal operating range.
Taking advantage of the functionalities of the smart meter (if it complies with the above measurement requirements), taking the measurements in a suitable period of time. The tests are considered valid if they are performed taking into account the operating conditions of the PV plant as specified in 4.4.1.1. Measurements with the methodology described in the previous paragraph must be performed after disconnecting the plant.
Evaluation of the Performance Tests
The current harmonic measurements should also be performed with an observation period of at least one week with fixed steps of 10 minutes. The values of the individual current components and the total harmonic current distortion must be given in tables in percentage of In and for the operation of the RRGP within the active power ranges and 75-100% of Pn. The individual harmonic current components shall be specified as subgroup values for frequencies up to 50 times the fundamental grid frequency, and the total harmonic current distortion shall be calculated as derived from this.
Current harmonics are measured for RRGP operating with reactive power as close to zero as possible, i.e.
Post-Connection Inspection
SAFETY INFORMATION FORM TO BE FILLED BY THE APPLICANT
