FORM 2
THE PATENTS ACT, 1970
(39 of 1970) The Patents Rules, 2003
COMPLETE SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION:
"False trip prevention of transformer due to Inrush current"
APPLICANT(s):

NAME NATIONALITY ADDRESS
1. SHRI INDIAN Ramdeo Tekdi, Gittikhadan, Katol
RAMDEOBABA Road, Nagpur-440013,
COLLEGE OF Maharashtra, India
ENGINEERING AND
MANAGEMENT
2. VINAYTUKARAM INDIAN Department of Electrical
BARHATE Engineering,
Shri Ramdeobaba College of
Engineering and Management,
Gittikhadan, Katol Road,
Nagpur-440013
Maharashtra , India
3. PREAMBLE TO THE DESCRIPTION:
PROVISIONAL COMPLETE
The following The following specification particularly describes
specification describes the invention and the manner in which it is to be
invention: performed:
Controller is used to A sample laboratory model of 5kVA transformer
monitor transformer considered for the evaluation of the proposed
primary current and methodology adopted for processing performance of methodology which is applicable

vis-a-vis to any power Transformer with appropriate changes in configuration of

components being used in this system. The
(Algorithm) detects proposed methodology used for detecting inrush
Inrush current and current by way of Dead Band (1) (as indicated by
issues a signal (Inrush "1" in Fig.1 and Fig.2 shown in detailed
flag) that blocks Description to be followed) identification is
relaying signals in configured with DSPIC controller which monitors
Differential Protection current in the primary winding of the transformer
Scheme of with Current Transducer (CTR)-LEM HXS 10-
transformer during NP/SP3.These components can be suitably
occurrence of the replaced as per requirement of the scheme where
Inrush current. ever it is proposed to be implemented by
observing only the scaling factor for controller
inputs. The nature of nonlinearity of Inrush current

has a significantly large magnitude but it contains
a "Dead Band (1)" (Time zone corresponding to
negligibly low instantaneous value over a period
of fixed one cycle of 50 Hz frequency).The
Controller continuously monitors current in
primary winding and blocks relaying signals to the
breaker during Inrush current which is detected by
the presence of the Dead Band (1) thereby
generating a Inrush Flag that implies presence of
inrush current. This Inrush Flag disables the
Differential Relay avoiding false tripping of the
Transformer durinq Inrush.
4. DESCRIPTION (Description shall start from next page):
"ATTACHED"
5. CLAIMS (not applicable for provisional specification. Claims should start
with the preamble - "l/We claim" on separate page)
"ATTACHED"
6. DATE AND SIGNATURE (to be given on the last page of specification)
7. ABSTRACT OF THE INVENTION (to be given along with complete
specification on a separate page)
"ATTACHED"

Name: 1) Dr. Vinay Tukaram Barhate
2) Mr. Sudarshan Rajesh Khond
Address: Department of Electrical Engineering,
Shri Ramdeobaba College of Engineering and
Management,
Gittikhadan, Katol Road,
Nagpur-440013
Maharashtra, India
Title: "False trip prevention of transformer due to
Inrush current"
Field of Invention: Electrical Power Systems Engineering.
Application of Invention: Protection of Transformers
Type: Utility patent
Description:
Background:
Power transformers are critical components in Power System from protection point of view considering their very high cost and systems dependency on them for continuity in power supply. To minimize the damage, power transformers are required to be taken out of operation when an internal fault occurs in them. Repairing a power transformer may be expensive affair and also power outage that is caused due to taking transformer out of service severely affects large electrical utilities. Consequently, it is of a great importance to minimize the frequency and duration of unwanted outages. Accordingly, high demands are imposed on power transformer protective relays. The requirements include dependability (no missing operations), security (no false tripping), and speed of operation (short fault clearing time)[l],[2]. Switching of power transformers may cause mal operation of differential relay protection scheme used for transformer protection. Switching of power Transformer also referred as charging of transformer when supply voltage sine wave passes through a 0 instantaneous value causes large magnetizing Inrush current to flow owing to very large requirement of flux. Transformer core saturates and current in primary winding is of peaky nature with time zones containing negligible instantaneous value referred as "Dead Zones". This high value of the primary current cause differential protection to sense Inrush current as internal fault condition and issue a trip signal which isn't desired as large magnitude of the inrush current goes on decreasing in every subsequent cycle of supply voltage eventually settling to its relatively low, nominal value [3].

To avoid false tripping of the transformer in Inrush condition (time period where magnitude of Inrush current is large enough to cause differential relay to issue trip signal), relays trip signal during inrush condition is required to be blocked [4]. To disable relay operation during Inrush condition, a signal is required to be generated which will restrain relay from operating. Method proposed is an innovative way of detecting Inrush current and hence blocking relaying signals during Inrush condition.
Object of Invention:
The main motive of the proposed method is to provide uninterrupted power flow, as it is of a great importance to minimize the frequency and duration of unwanted outages of Power transformer. Therefore the main objective is to establish a method by which Inrush current in transformer can be detected and hence false trip of differential relay protecting Power Transformer due to Inrush can be avoided.
Statement of Invention:
New method for Inrush current detection in Power transformer is claimed. Underlying method achieves efficient detection of Inrush current and doesn't require any additional hardware equipment e.g. Rogowski coil [8].
A summary of Invention
A 5kVA Transformer is energized at different switching Instances on no load condition and waveform of current is observed. It is found that the current waveforms are peaky in nature with low values for considerable amount of time in every cycle whenever Transformer was switched at instant other than the one corresponding to the peak of supply voltage sine wave [5]. An algorithm was developed which could use this feature of current to detect presence of Inrush in current. Code used for detection of Inrush defines "Dead Band (1)" as the time period in each cycle during which the instantaneous current magnitude is negligibly low. If this "Dead Band (1)" occurs for a longer duration, algorithm detects current as "Inrush Current'' and sets Inrush flag that disables differential relay operation. This method uses continuous monitoring of current and differential relay operation in enabled once Inrush in a current dies out. In this unique type of protection scheme, both the task of detecting Inrush current and differential relay protection are achieved with the help of controller [6]. For differential protection, method utilizes Fuzzy logic that takes mean of primary and secondary current called Restraining Current(IRestraining) and difference of primary and secondary currents called Differential Current (IDifferential) as Fuzzy inputs and based on the

particular rule fired according to the knowledge base, gives trip/No trip signal. This Fuzzy logic algorithm is triggered only if Inrush flag is set to Low [7].
Invention:
With the help of proposed method, Transformer Inrush current is efficiently detected and differential protection is bypassed during such condition. Proposed method is tested on 5kVA Transformer. Method also achieves differential protection with the Fuzzy logic algorithm code embedded with Controller that is enabled only when Inrush in the current is not present.
Brief Description:
With the help of controller, primary winding current in a transformer is continuously monitored. For various switching instances, current is measured and checked for the presence of the "Dead Band (1)" i.e. lows in instantaneous current waveform and time period for the same is measured. If the measured time period equivalent value comes out to be greater than the value specified for peaky Inrush current, Fuzzy logic algorithm for differential relay protection is disabled hence false trip of the transformer due core saturation/Inrush is avoided.
Detailed Description:
Main motive of this research work is to examine the actual nature of Inrush current as always been read and seen in the literature [8]. Therefore to verify the nature of inrush empirically the laboratory model of three phases 5 KVA Transformer is chosen for experimentation for observing inrush current by monitoring the current in primary winding when Transformer is switched randomly on no load at hundreds of instances. The typical and symbolic samples of Inrush current waveform out of hundreds of instances are shown in Fig.1 and Fig.2 representing sample for positive and negative inrush.
A Dead Band is observed in both the cases i.e. in Positive inrush as well as in Negative inrush current which is indicated as "1" in Fig.l and Fig.2. respectively. These Dead Band (1) in primary current are defined as the one having very low instantaneous values of the current for a considerable amount of time period per cycle for 50Hz frequency (Standard supply frequency).
The method presented here uses DSPIC controller to monitor current in primary winding of the power Transformer which is scaled down with the help of current transducer LEM HXS 10-NP/SP3 for 5kVA transformer.

If primary current is sinusoidal in nature, algorithm does not categorize it as the one containing Dead Band (1) as low value of primary current does not appear for the duration defined in the Dead Band (1) in the code for Inrush detection. However Inrush current containing such low values for duration more than defined in the Dead Band (1) is detected by the algorithm. As long as current contains Dead Band (1), relay operation is disabled and the same is enabled once current is found to be free from Dead Band (1) which is assumed to be current other that magnetizing Inrush current. In this way, property of Inrush current which exhibits nature of current having low values for relatively longer duration per cycle is utilized for the detection of Inrush current and prevention of false.
"Inrush flag55 is set by the controller which disables relaying signals as shown in Flow chart of Fig.3. Differential protection is also achieved with the proposed scheme using fuzzy logic which takes inputs as Idifferential (difference of primary and secondary currents) and Irestraining (average of primary and secondary winding currents). Trip signal is issued based on subsequent firing of corresponding Fuzzy Rule in which differential current measured by the controller comes out to be more than the restraining current. Percentage of the slope can be changed by changing scaling factor.
64 samples are taken for calculation for every sine wave. If Dead Band (1) occurs for 14 samples or more, Current is classified as Inrush. For Dead Band (1) occurring for less than 14 samples, wave is classified as one free from inrush.
References:
[1] Dr. Vinay Barhate, Dr. K.L. Thakre and Dr. S.S. Limaye, "Adoptive Combined Neuro-Fuzzy Approach for enhancement of Reliability in Transformer Protection55, a Ph.D thesis submitted and evaluated by Rashtrasant Tukdoji Maharaj Nagpur University, October, 2016
[2] Bogdan Kasztenny and Mladen Kezunovic, "Improved power transformer protection using Numerical relays55, A report of Authors at Texas A&M University, USA
[3] Y.G.Paithankar, S.R.Bhide, "Fundamentals of Power System Protection55, PHI Learning Pvt Ltd publishers, 2013, pp 66-76 & 77-103
[4] IEEE Std C37.91-2000, "IEEE Guide for Protective Relay Applications to Power Transformers55, Sponsored by Power Systems

Relay Committee of the IEEE Power Engineering Society , Approved on 8 March 2000 by IEEE-SA Standards Board.
[5] B. Ravindranath, M. Chander, "Power System Protection and Switchgear" ,New Age International Publishers, 2012, pp 123-135
[6] V.T.Barhate, Dr.K.L. Thakre, Dr. S.S.Limaye, "Intelligent Transformer faults monitoring System", International Conference on Advanced Computing &Communication Technologies, ICACCT-2008, Panipat, November 8-9, 2008.
[7] V.T.Barhate, Dr. K.L. Thakre, Dr. S.S.Limaye, "Fuzzy Logic an alternate tool for protection against internal faults in transformer", International conference on Advanced Computing & Communication Technologies, ICACCT-2007 Panipat, November 3-4, 2007.
[8] Ljubomir A. Kojovic, Martin T. Bishop, Timothy R. Day, Oak Creek, Racine, "Transformer Inrush current detector", a US Patent Application Publication no. US20090147412A1, publication Date June 11, 2009.

Claims:
1. Method adopted here effectively detects Inrush current and blocks relaying signals to the circuit breaker during Inrush with the help of controller and Current Transducer only. Thus the method requires lesser hardware components and lesser mechanism without compromising on reliability. 2. Methodology claims that a false tripping of transformer due to Inrush is avoided even if transformer is charged at any instant of switching on sine wave of supply voltage. 3.. Method uses innovative way of differential protection of transformer with Fuzzy Logic code in controller, which can be improvised at any point of time in future, making this method open for customization as and when required by the supply utility companies based on various Power Transformer ratings with suitable Current Transformer paired with Current Transducer.