What is Voltage Drop Study?
Voltage drop study and analysis is activity to determine and analyze voltage and voltage drops profile in electricity circuit and network during normal and emergency operations. Voltage drop study is one of Power System Study series which usually include in Load Flow Study and Analysis. Voltage drop study is one of the most basic and commonly needed electrical study. This study also has relation to cable specification design and Power Quality Study — Omazaki Engineering is a consultant who serves voltage drop studies and analysis consulting services. If you are looking for voltage drop analysis study consultants company, for your new project or existing electricity systems evaluation in Indonesia and South East Asia, contact Omazaki Engineering by sending an email to firstname.lastname@example.org or filling in the form in contact. We conduct voltage drop study analysis and evaluation using ETAP software.
What is Voltage Drop?
By definition, voltage is the measurement for the electrical force between two points that drives the current. And, voltage drop is the amount of voltage loss that occurs through all or part of the circuit due to impedance. It is undeniable. A voltage drop in an electrical circuit normally occurs when a current passes through the cable. It is related to the resistance or impedance to current flow with passive elements in the circuits including cables, contacts and connectors affecting the level of voltage drop. The longer the circuit or length of cable the greater the voltage loss.
How to Know the Amount of Voltage Drop?
There are two ways to know amount of voltage drop:
- Mathematical calculation
Basic formula of voltage drop for three phase system based on IEEE Std 141:
- Vd = Voltage drop per phase, volts
- V = sending end line-to-line voltage
- R = rl, where r is the unit resistance in Ω/km
- X = xl, where x is the unit reactance in Ω/km
Allowable Voltage Drops
Percentage of maximum allowable voltage drop varies from country to country. Typical values for the percentage of permissible voltage drop for low voltage (LV) installations are given below.
Percentage of allowable voltage drop according to IEC 60364-5-52:
NFPA 70 – NEC 2017 Standard
Percentage of maximum voltage drop according to NFPA 70 – NEC 2017:
- Branch circuits — Maximum voltage drop of 3%. The maximum total voltage drop when combining both the branch circuit and feeder shouldn’t exceed 5% [210-19(a) FPN No. 4].
- Feeders — Maximum voltage drop of 3%. The maximum to-tal drop for a combination of branch circuit and feeder should not exceed 5% [215-2(d) FPN No. 2].
- Services — There’s no recommended voltage drop for service conductors in the NEC
- Phase converters –Should not exceed 3% [455-6(a) FPN].
- Recreational vehicle parks –Mximum voltage drop for branch circuit conductors should not exceed 3%, while the combination voltage drop of the branch circuit and feeder should not exceed 5% of the voltage source [210-19(a) FPN No. 4 and 551-73(d) FPN].
What Causes of Excessive Voltage Drop?
There are various causes of excessive voltage drop, including:
- Poor engineering design or previously no engineering design that meets recognized standards
- Incorrect conductor size (undersized)
- Actual diameter and length of conductor do not match
- Improper cable conducting material
- Improper use – Actual load current is higher than design circuit current
- Bad connection (termination)
- Connecting too many cables to one cable lug
- Using an unapproved connector
- Connect two conductors of different materials in an unapproved connector (such as copper and aluminum)
- Failure to tighten lugs or screws to rated standards
What Can Go Wrong with Voltage Drop?
The negative impact of excessive voltage drop can cause problems such as motor running slowly, heater not heating up to its full potential, dim lighting. To compensate for the voltage drop, larger cross-sectional cables can be used which offer less resistance / impedance to the flow of current.
- Motors can’t start up — Appliances that require higher in-rush current levels may not start up as the voltage is below their minimum operating power level. Voltage drop needs to be taken into account when designing circuits for motors including MCA vs FLA parameters.
- Intermittent operation — If an appliance does start up, it may shut down when it detects a noticeable voltage drop. This will usually happen to computers & gaming systems during ‘that perfect high-scoring game’. Customers expect reliable power systems.
- Inconsistent lighting levels — Street lighting design must take into account the gradual reduction in voltage level as a 5% drop in voltage can be noticeable on lighting levels.
- Blown Fuses & Tripping Circuit Breakers — Remember that P=VI so if V is low, an appliance may increase its I to reach its desired power level. When multiple loads on a circuit increase their current consumption, it could cause the safety mechanism to trip.
- Increased current consumption may cause motors and ballasts to overheat and reduce their operating life. Resistive loads such as heaters & incandescent lights will also have a reduced life span. Fluctuating voltage levels caused by other loads on the system may cause an annoying flicker.
Why We Need to Conduct Voltage Drop Analysis Study?
- Major change — Voltage drop analysis study should be performed anytime major changes are made to the electricity system
- System efficiency — If a circuit supports much of a load, a larger conductor will pay for itself many times over in energy savings alone.
- System performance — Some loads perform best when voltage drop is minimal.
- Troubleshooting — If you follow the allowable voltage drop recommendations, you don’t have to guess whether your field measurements indicate a problem or if the voltage is low due to not accommodating voltage drop in the design.
- Load protection — Under-voltage for inductive loads can cause overheating, inefficiency, and shorter life span of equipment.
Objectives of Voltage Drop Studies
The objectives of the voltage drop analysis study include:
- To comply with applicable electricity standards and regulations
- To meet the essential operational requirements so that the system performance will improve
- To reduce power losses so that energy effectiveness and efficiency are increased
How To Conduct Voltage Drop Analysis Study
There are two methods in the study and analysis of voltage drop:
- Manual calculation
- Engineering software
Voltage Drop Analysis Using Software
Procedure of The Study
- Data collection and verification
- System modelling
- Model verification and validation
- Analysis and Recommendation
Data Requirement for Voltage Drop Studies
- Nominal kV
- Phase angle
- Load diversity factor
- Branch includes three-winding transformer, two-winding transformer, transmission line, cable, reactor, and impedance.
- Branch data also includes Branch Z, R, X, or X/R values and units, tolerance, and temperatures, if applicable
- Cable and transmission line length and unit
- Transformer rated kV and kVA, tap and load tap-changing (LTC) settings
- Impedance base kV and base kVA
Static Load Data
- Rated kV, kVA, and power factor
- Operating load
Lumped Load Data
- Rated kV, kVA, and power factor
- Operating load
Study Deliverables and Reporting
After carrying out the study, a report should be produced by the individual or voltage drop analysis consultants in the format preferred by the client or users. A detailed report is provided that includes:
- A full description of the basis, purpose and scope of the study
- Tabulations of the data used to model system components and a corresponding one-line diagram
- Descriptions of the scenarios evaluated and identification of the scenario used to evaluate load flow
- The tabulation identifies bus voltage, voltage angle, and voltage drop at each bus; branch voltage drop, power flow in kW, kVAR, kVA, Amps and power factor; branch loss in kW, kVAR, kVA, and total system losses
Contact Omazaki Engineering if you are looking for a voltage drop study analysis and evaluation consulting service by consultant to help you with new project or your existing electrical system in Indonesia and South East Asia.
- Power System Study & Analysis
- Load Flow Study & Analysis
- Protection Coordination Study
- Motor Starting Study and Analysis
- Power System Transient Stability Study
- Harmonic Study and Analysis
- Arc Flash Study & Assessment
- Power Quality Study & Assessment
- Voltage Imbalance (Unbalance) Study
- IEC 60364-5-52 Low-voltage electrical installations – Part 5-52: Selection and erection of electrical equipment – Wiring systems
- IEEE Std 141-1993 Recommended Practice for Electric Power Distribution for Industrial Plants
- NFPA 70 – National Electric Codes 2017